Cost effective synthesis of oxide materials for lithium ion batteries

ABSTRACT

Methods for synthesizing single crystalline Ni-rich cathode materials are disclosed. The Ni-rich cathode material may have a formula LiNiXMnyMzCo1-x-y-zO2, where M represents one or more dopant metals, x≥0.6, 0.01≤y&lt;0.2, 0≤z≤0.05, and x+y+z≤1.0. The methods are cost-effective, and include methods for solid-state, molten-salt, and flash-sintering syntheses.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the earlier filing date of U.S.Provisional Application No. 63/028,146, filed May 21, 2020, and U.S.Provisional Application No. 63/020,621, filed May 6, 2020, each of whichis incorporated by reference in its entirety herein.

ACKNOWLEDGMENT OF GOVERNMENT SUPPORT

This invention was made with Government support under ContractDE-AC05-76RL01830 awarded by the U.S. Department of Energy. TheGovernment has certain rights in the invention.

FIELD

Methods of synthesizing crystalline oxide materials are disclosed, aswell as cathodes including the crystalline oxide materials and lithiumion batteries including the cathodes.

SUMMARY

Embodiments of methods for synthesizing crystalline oxide materials aredisclosed. Cathodes including the crystalline oxide materials andlithium ion batteries including the cathodes also are disclosed.

In some embodiments, a solid-state method includes makingmonocrystalline lithium nickel manganese cobalt oxide by: heating asolid hydroxide precursor comprising Ni_(X)Mn_(y)M_(z)Co_(1-x-y-z)(OH)₂at a temperature T_(S1) in an oxygen-containing atmosphere for aneffective period of time t₁ to convert the solid hydroxide precursor toa solid oxide precursor, where M represents one or more dopant metals,x≥0.6, 0.01≤y<0.2, 0≤z≤0.05, and x+y+z≤1.0; combining the solid oxideprecursor with a molar excess of a lithium compound; heating the solidoxide precursor and the lithium compound at a temperature T_(S2) for aneffective period of time t₂ to produce a first product; cooling thefirst product to ambient temperature; reducing a mean particle size ofthe first product to 0.1 μm to 10 μm; heating the first product havingthe reduced mean particle size at a temperature T_(S3) for an effectiveperiod of time t₃ to produce a second product; cooling the secondproduct to ambient temperature; reducing a mean particle size of thesecond product to 0.1 μm to 10 μm; and heating the second product havingthe reduced mean particle size at a temperature T_(S4) for an effectiveperiod of time t₄ to produce monocrystalline lithium nickel manganesecobalt oxide having a formula LiNi_(X)Mn_(y)M_(z)Co_(1-x-y-z)O₂.

In some embodiments, a molten-state method includes makingmonocrystalline lithium nickel manganese cobalt oxide by: heating asolid hydroxide precursor comprising Ni_(X)Mn_(y)M_(z)Co_(1-x-y-z)(OH)₂at a temperature T_(M1) in an oxygen-containing atmosphere for aneffective period of time t₁ to convert the solid hydroxide precursor toa solid oxide precursor, where M represents one or more dopant metals,x≥0.6, 0.01≤y<0.2, 0≤z≤0.05, and x+y+z≤1.0; combining the solid oxideprecursor with a molar excess of a lithium compound and a sinteringagent to form a mixture; combining the solid oxide precursor with amolar excess of a lithium compound and a sintering agent to form amixture; heating the mixture in an oxygen-containing atmosphere at atemperature T_(M2) for a period of time t₂; increasing the temperatureto a temperature T_(M3), wherein the temperature T_(M3)>the temperatureT_(M2), and heating the mixture at the temperature T_(M3) for a periodof time t₃ to produce a first product and the sintering agent;separating the sintering agent from the first product; drying the firstproduct; and heating the first product in an oxygen-containingatmosphere at a temperature T_(M4) for an effective period of time t₄ toproduce monocrystalline lithium nickel manganese cobalt oxide having aformula LiNi_(X)Mn_(y)M_(z)Co_(1-x-y-z)O₂.

In some embodiments, a flash-sintering method includes makingmonocrystalline lithium nickel manganese cobalt oxide by: combining asolid hydroxide precursor comprising Ni_(X)Mn_(y)M_(z)Co_(1-x-y-z)(OH)₂with a molar excess of a lithium compound to form a hydroxide mixture,where M represents one or more dopant metals, x≥0.6, 0.01≤y<0.2,0≤z≤0.05, and x+y+z≤1.0; heating the hydroxide mixture in anoxygen-containing atmosphere at a temperature T_(F1) for an effectiveperiod of time t₁ to form an oxide mixture comprising oxides of nickel,manganese, cobalt, lithium, and, if present, the one or more dopantmetals, or a combination thereof; increasing the temperature to atemperature T_(F2) at a rate of ≥10° C./min; and heating the oxidemixture in an oxygen-containing atmosphere at the temperature T_(F2) foran effective period of time t₂ to form monocrystalline lithium nickelmanganese cobalt oxide having a formulaLiNi_(X)Mn_(y)M_(z)Co_(1-x-y-z)O₂.

In any of the foregoing embodiments, the solid hydroxide precursor maybe prepared by: preparing a 1.5-2.5 M solution comprising metal salts inwater, the metal salts comprising a nickel (II) salt, a manganese (II)salt, a cobalt (II) salt, and optionally one or more dopant metal salts,wherein a mole fraction x of the nickel (II) salt in the solution is≥0.6, a mole fraction y of the manganese (II) salt is 0.01≤y<0.2, a molefraction z of the one or more dopant metal salts is 0≤z≤0.05, a molefraction of the cobalt (II) salt is 1−x−y−z, and x+y+z≤1.0; combiningthe solution comprising metal salts in water with aqueous NH₃ andaqueous NaOH or KOH to provide a combined solution having a pH of10.5-12 and a combined metal salt concentration of 0.1 M to 3 M; agingthe combined solution for 5 hours to 48 hours at a temperature of 25° C.to 80° C. to co-precipitate hydroxides of nickel, manganese, and cobaltto provide the solid hydroxide precursor; and drying the solid hydroxideprecursor, wherein the solid hydroxide precursor comprises particleshaving a mean particle size of 0.5 μm to 2.5 μm.

In some embodiments, a cathode comprises monocrystallineLiNi_(X)Mn_(y)M_(z)Co_(1-x-y-z)O₂ wherein M represents one or moredopant metals; x≥0.6, 0.01≤y<0.2, z≤0.05, and x+y+z≤1.0; and a meanparticle size of the monocrystalline LiNi_(X)Mn_(y)M_(z)Co_(1-x-y-z)O₂is 0.5 μm to 5 μm.

In some embodiments, a battery system includes the cathode, an anode, anelectrolyte, and a separator positioned between the anode and thecathode.

The foregoing and other objects, features, and advantages of theinvention will become more apparent from the following detaileddescription, which proceeds with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

FIG. 1 is a schematic diagram of one embodiment of a method for making anickel manganese cobalt hydroxide precursor.

FIG. 2 is a schematic diagram of one embodiment of a solid-state methodfor making monocrystalline lithium nickel manganese cobalt oxide.

FIG. 3 is a schematic diagram of one embodiment of a molten salt methodfor making monocrystalline lithium nickel manganese cobalt oxide.

FIG. 4 is a schematic diagram of one embodiment of a flash-sinteringmethod for making monocrystalline lithium nickel manganese cobalt oxide.

FIG. 5 is a schematic diagram of an exemplary lithium ion battery.

FIG. 6 is a schematic side elevation view of a simplified pouch cell.

FIGS. 7A-7H show characterization of single crystallineLiNi_(0.76)M_(0.14)C_(0.1)O₂ (NMC76).

FIG. 7A is a scanning electron microscope (SEM) image of singlecrystalline NMC76. FIG. 7B is a cross-section image of singlecrystalline NMC76. FIG. 7C is a selected area electron diffraction(SAED) pattern of single crystalline NMC76. FIG. 7D shows synchrotronX-ray diffraction and Rietveld refinement patterns. FIG. 7E is ahigh-resolution HAADF-STEM (high-angular dark-field scanningtransmission electron microscopy) image of single crystalline NMC76(corresponding to the square in FIG. 7B). FIG. 7F is ahigher-magnification image of the corresponding boxed region in FIG. 7E.FIG. 7G shows EDS (energy-dispersive x-ray spectroscopy) elementalmapping of Ni, Mn, Co, and O. FIG. 7H is an EDS overlapped image withline scanning showing the elemental distribution intensity.

FIGS. 8A-8F show characterization of a NMC76 secondary (polycrystalline)particle. FIG. 8A is a cross-section image. FIG. 8B shows SAED results.FIG. 8C is an HRTEM image of a primary particle. FIGS. 8D and 8E areHRTEM images of surface structure. FIG. 8F is an HRTEM image of a grainboundary.

FIG. 9 shows cyclic voltammetry curves of single crystalline NMC76 indifferent voltage windows using Li metal as the anode; scanning rate 0.1mV/s.

FIG. 10 shows cycling stability of single crystalline NMC76 withdifferent areal density between 2.7 and 4.5 V in half cells using Limetal as anode. Charge at 0.1 C and discharge at 0.33 C.

FIG. 11 shows initial charge-discharge curves between different cutoffvoltages at 0.1 C using Li metal as anode. Discharge capacity at 4.3,4.4 and 4.5 V cutoff voltage are 184.9, 194.1 and 203.1 mAh/g,respectively.

FIGS. 12A-12C show electrochemical performance of single crystallineNMC76 at 4.2 V cutoff (12A), 4.3 V cutoff (12B), and 4.4 V cutoff (12C)tested in a full cell using graphite as the anode.

FIGS. 13A-13C show the corresponding charge-discharge curves of thecells in FIGS. 12A-12C, and accompanying SEM images of the singlecrystalline NMC76 after cycling.

FIGS. 14A-14B show an initial charge-discharge curve of single crystalNMC76 between 2.7-4.2 V (vs. graphite) (14A), and the middle voltage ofthe charge-discharge curves and the voltage difference over 200 cycles(14B).

FIGS. 15A-15B show an initial charge-discharge curve of single crystalNMC76 between 2.7-4.3 V (vs. graphite) (15A), and the middle voltage ofthe charge-discharge curves and the voltage difference over 200 cycles(15B).

FIGS. 16A-16B show an initial charge-discharge curve of single crystalNMC76 between 2.7-4.4 V (vs. graphite) (16A), and the middle voltage ofthe charge-discharge curves and the voltage difference over 200 cycles(16B).

FIGS. 17A-17F are SEM images of single crystal NMC76 after cyclingtests: 2.7-4.2 V vs. graphite (17A-B); 2.7-4.3 V vs. graphite (17C-D);2.7-4.4 V vs. graphite (17E-F).

FIGS. 18A-18L show the morphology and structure study of singlecrystalline NMC76. (18A) SEM image of single crystalline NMC76 after 200cycles. (18B) Cross-section STEM bright field image of singlecrystalline NMC76 after 200 cycles. (18C) STEM bright field image ofinternal slicing. (18D) STEM-HAADF image around slicing area. Upperinset is zoomed image of gliding area. (18E) SAED of gliding area. (18F)EELS mapping of selected area in (18B). (18G) SEM images of singlecrystalline NMC76 initially charged to 4.8 V (vs. Li⁺/Li). (18H) SEMimages of single crystalline NMC76 discharged to 2.7 V (after beingcharged to 4.8 V vs. □+/□). (18I-J) STEM images of single crystallineNMC76 at 4.4 V charge status (cycled in a full cell between 2.7-4.4 Vfor 120 cycles). (18K-L) STEM images of single crystalline NMC76 atdischarge status (cycled in full cell between 2.7-4.4 V for 120 cycles).

FIG. 19 shows SEM images of single crystals on the same electrode beforecycling. Eight different regions are randomly selected and analyzed inthe SEM images 1-8. No pre-existing “gliding” lines are presenting inthe pristine single crystalline NMC76.

FIG. 20 shows SEM images of single crystalline NMC76 located at eightdifferent locations of the same electrode after 120 cycles (2.7-4.4 Vvs. graphite). Gliding steps are obviously observed on cycled singlecrystals.

FIG. 21 shows SEM images of single crystalline NMC76 located at eightdifferent locations of the same electrode after 200 cycles (between2.7-4.4 V vs. graphite).

FIG. 22 shows electron energy loss spectra of O K-edge, Ni L-edge, MnL-edge, and Co L-edge, EELS that correspond to test points 1-6 in FIG.18B.

FIGS. 23A and 23B are SEM images of single crystalline NMC76 charged to4.8 V (vs. Li⁺/Li) (23A), and discharged to 2.7 V after charging to 4.8V (23B).

FIGS. 24A-24D are STEM images of single crystalline NMC76 after 120cycles at charged status (cycled between 2.2-4.4 V vs. graphite). FIG.24A is a cross-sectional image of the cycled single crystal. FIG. 24B isa STEM image of the boxed region in FIG. 24A. FIGS. 24C-24D are STEMimages of the lower (24C) and upper (24D) tip regions around internalmicro-cracks at the charged status.

FIGS. 25A-25E are STEM images of single crystalline NMC76 after 120cycles at discharge state (cycled between 2.2-4.4 V vs. graphite). FIG.25A is a cross-sectional image of the cycled single crystalline NMC76.FIG. 25B is a STEM image of the cycled single crystalline NMC76. FIG.25C is a STEM bright field image of the boxed area of FIG. 25B. FIG. 25Dis a STEM-HAADF image of the boxed area. FIG. 25E is a comparison of twoselected areas from FIG. 25D.

FIGS. 26A-26F show surface structure and morphology evolution by in situAFM and mechanical analysis for single crystalline NMC76. FIG. 26A is anAFM image at OCV state. FIGS. 26B-26C are a comparison of selectedsurface evolution during in situ AFM testing. FIG. 26D shows COMSOLsimulated shear stress along the yz direction during charge(delithiation) at scaled time of 0.1 T. FIG. 26E shows COMSOL simulatedshear stress along the yz direction during discharge (lithiation) atscaled time of 0.1 T. FIG. 26F is a schematic illustration of structuralevolution of single crystalline NMC76 upon cycling.

FIGS. 27A and 27B are graphs showing gliding step width vs. testing time(FIG. 27A), and gliding step width vs. voltage (FIG. 27B).

FIGS. 28A-28D show the time evolution of Li concentration and stressduring the de-lithiation process. FIG. 28A shows the Li concentrationgradient in the de-lithiation process. FIGS. 28B-28D show radial stress(28B), tangential stress (28C), and axial stress (28D) distribution atdifferent times.

FIGS. 29A-29D show the time evolution of Li concentration and stressduring the lithiation process. FIG. 29A shows the Li concentrationgradient in the lithiation process. FIGS. 29B-29D show radial stress(29B), tangential stress (29C), and axial stress (29D) distribution atdifferent times.

FIGS. 30A-30C are SEM images and STEM images of single crystalline NMC76showing microcracks, which propagate from the center to the surface,forming fractures.

FIGS. 31A-31D show the elastic stress tensor in the local Cartesiancoordinate system on the yz plane at a scaled time of 0.1 T solvednumerically by the COMSOL model. FIG. 31A shows the normal stress alongthe zz direction, which will be responsible for crack opening along(003) direction, during delithiation (charging). FIG. 31B shows theshear stress along the yz direction, which is responsible for gliding,during delithiation (charging). FIG. 31C shows the shear stress alongthe yz direction during lithiation (discharging). FIG. 31D shows theshear stress along the yz direction during lithiation (discharging) withanisotropic strain.

FIG. 32 shows an SEM image of a 20 μm single crystal NMC76 and imagesobtained by in situ AFM.

FIGS. 33A-33D are SEM images of pristine Ni_(0.76)Mn_(0.14)Co_(0.1)(OH)₂(33A), and oxides prepared by heating theNi_(0.76)Mn_(0.14)Co_(0.1)(OH)₂ for 15 hours at 800° C. (33B), 900° C.(33C), or 1000° C. (33D).

FIG. 34 is a schematic diagram showing one embodiment of a molten-saltprocess as disclosed herein, as well as SEM images of the hydroxideprecursor, the oxide precursor, and the single crystalLiNi_(0.76)Mn_(0.14)Co_(0.1)O₂.

FIGS. 35A and 35B are SEM images of Ni_(0.76)Mn_(0.14)Co_(0.1)O₂prepared without NaCl (35A) and with NaCl (35B).

FIGS. 36A-36C show the initial charge-discharge curve ofLiNi_(0.76)Mn_(0.14)Co_(0.1)O₂ prepared with and without NaCl (36A), thecycling stability of a single crystal NMC76 electrode (20 mg/cm²) in afull cell using graphite as the anode between 2.7-4.2V, charge at 0.1 Cand discharge at 0.33 C (36B), and the cycling stability of a singlecrystal NMC76 electrode (21.5 mg/cm²) in a full cell using graphite asthe anode between 2.7-4.3V. 1 C=200 mA/g (36C).

FIGS. 37A-37C are SEM images of LiNi_(0.7)Mn_(0.22)Co_(0.08)O₂ washedwith water (37A) and formamide (FM) (37B), and the initialcharge-discharge curves of the samples (37C).

FIG. 38 is a schematic diagram comparing synthesis processes forpolycrystalline and monocrystalline LiNi_(X)Mn_(y)Co_(1-x-y)O₂.

FIGS. 39A-39C are SEM images of LiNi_(0.76)Mn_(0.14)Co_(0.1)O₂ preparedby flash sintering at ramping rates of 2° C./min (39A), 10° C./min(39B), and 20° C./min (39C).

FIGS. 40A-40B are SEM images of LiNi_(0.76)Mn_(0.14)Co_(0.1)O₂ preparedwithout preheating (40A) or with preheating (40B) prior to flashsintering.

FIG. 41 shows the charge-discharge curves of the flash-sinteredLiNi_(0.76)Mn_(0.14)Co_(0.1)O₂ of FIGS. 40A and 40B.

FIGS. 42A-42C are SEM images of Ni_(0.76)Mn_(0.14)Co_(0.1)(OH)₂ (42A),oxide precursor (42B), and single crystal LiNi_(0.76)Mn_(0.14)Co_(0.1)O₂(42C) prepared by a solid-state method as disclosed herein.

FIG. 43 shows charge-discharge curves of theLiNi_(0.76)Mn_(0.14)Co_(0.1)O₂ of FIG. 42C.

FIGS. 44A and 44B show the charge-discharge curves of aLiNi_(0.76)Mn_(0.14)Co_(0.1)O₂ cathode prepared by a molten-saltsynthesis as disclosed herein (44A) and an SEM image of theLiNi_(0.76)Mn_(0.14)Co_(0.1)O₂ (44B).

FIGS. 45A and 45B show the charge-discharge curves of aLiNi_(0.76)Mn_(0.14)Co_(0.1)O₂ cathode prepared by a molten-saltsynthesis as disclosed herein (45A) and an SEM image of theLiNi_(0.76)Mn_(0.14)Co_(0.1)O₂ (45B).

FIG. 46 shows SEM, HRTEM, and SAED images of single crystalLiNi_(0.76)Mn_(0.12)Co_(0.1) Mg_(0.01)Ti_(0.01)O₂.

FIGS. 47A and 47B are x-ray diffraction patterns comparingLiNi_(0.76)Mn_(0.14)Co_(0.1)O₂ and LiNi_(0.76)Mn_(0.12)Co_(0.1)Mg_(0.01)Ti_(0.01)O₂.

FIGS. 48A and 48B compare the charge-discharge curves (48A) and cyclingstability (48B) of LiNi_(0.76)Mn_(0.14)Co_(0.1)O₂ andLiNi_(0.76)Mn_(0.12)Co_(0.1)Mg_(0.01)Ti_(0.01)O₂.

FIG. 49 is an SEM image ofLiNi_(0.76)Mn_(0.12)Co_(0.1)Mg_(0.01)Ti_(0.01)O₂ after cycling.

DETAILED DESCRIPTION

Nickel-rich lithium-manganese-cobalt oxide (NMC) cathodes(LiNi_(X)Mn_(y)Co_(1-x-y)O₂) are promising cathodes for next-generationlithium ion batteries. Such batteries may be used, for example, forlong-range electrical vehicles. In particular, NMC cathodes where x≥0.6,the capacity is ≥200 mAh/g, and the cathode is operable at high voltage(>3.8V) are desirable.

Traditionally, NMC cathodes are prepared by coprecipitation withaggregation of nano-sized primary particles into micro-sized secondarypolycrystalline particles. This aggregated particle structure shortensthe diffusion length of the primary particles and increases the numberof pores and grain boundaries within the secondary particles, whichaccelerate the electrochemical reaction and improves the rate capabilityof NMC. Secondary micron-sized particles formed of agglomeratednano-sized primary particles are the most common morphology forconventional NMC cathodes. However, as the Ni content increases above0.6, challenges arise. For example, such Ni-rich NMC cathodes aresubject to moisture sensitivity, aggressive side reactions, and/or gasgeneration during cycling, raising safety concerns. These challenges areattributable to the large surface area of the secondary particles.Additionally, while creating spherical-secondary polycrystalline NMCparticles reduces the surface/volume ratio, pulverization along the weakinternal grain boundaries is generally observed after cycling. Thesecracks are induced by the non-uniform volume change of primary particlesduring cycling and exacerbated by the anisotropy among individualparticles and grains in the polycrystalline NMC. The intergranularcracking exposes new surfaces to electrolyte for side reactions, whichaccelerates cell degradation. As the Ni content becomes ≥0.8 in NMC, themajor challenge in Ni-rich NMC cathodes becomes quite different fromthose in conventional NMC. For example, NMC811 is very sensitive tomoisture, which creates challenges for manufacturing, storing andtransporting the Ni-rich NMC. After extensive cycling gas generation bythe side reactions raises safety concerns.

This disclosure concerns embodiments of methods for synthesizing singlecrystalline Ni-rich cathode materials. Some embodiments of the disclosedmethods may be used for synthesizing large batches, e.g., 1 kg or more,of single crystal lithium nickel manganese cobalt oxide. In someembodiments, the single crystalline Ni-rich cathodes comprisemonocrystalline lithium nickel manganese cobalt oxide. In certainembodiments, single crystalline cathodes include reduced surface areas,phase boundaries, and/or more integrated crystal structures compared topolycrystalline cathodes. Advantageously some embodiments of the singlecrystalline Ni-rich cathodes demonstrate reduced gassing and/or particlecracking along grain boundaries during cycling. In some embodiments, themonocrystalline lithium nickel manganese cobalt oxide has a formulaLiNi_(X)Mn_(y)M_(z)Co_(1-x-y-z)O₂, where M represents one or more dopantmetals, x≥0.6, 0.02≤y<0.2, 0≤z≤0.05, and x+y+z≤1.0. In certainembodiments, the formula is Ni_(x)Mn_(y)Co_(1-x-y)O₂ where x≥0.6,0.02≤y<0.2, and x+y≤1.0.

I. Definitions and Abbreviations

The following explanations of terms and abbreviations are provided tobetter describe the present disclosure and to guide those of ordinaryskill in the art in the practice of the present disclosure. As usedherein, “comprising” means “including” and the singular forms “a” or“an” or “the” include plural references unless the context clearlydictates otherwise. The term “or” refers to a single element of statedalternative elements or a combination of two or more elements, unlessthe context clearly indicates otherwise.

Unless explained otherwise, all technical and scientific terms usedherein have the same meaning as commonly understood to one of ordinaryskill in the art to which this disclosure belongs. Although methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of the present disclosure, suitable methods andmaterials are described below. The materials, methods, and examples areillustrative only and not intended to be limiting. Other features of thedisclosure are apparent from the following detailed description and theclaims.

The disclosure of numerical ranges should be understood as referring toeach discrete point within the range, inclusive of endpoints, unlessotherwise noted. Unless otherwise indicated, all numbers expressingquantities of components, molecular weights, percentages, temperatures,times, and so forth, as used in the specification or claims are to beunderstood as being modified by the term “about.” Accordingly, unlessotherwise implicitly or explicitly indicated, or unless the context isproperly understood by a person of ordinary skill in the art to have amore definitive construction, the numerical parameters set forth areapproximations that may depend on the desired properties sought and/orlimits of detection under standard test conditions/methods as known tothose of ordinary skill in the art. When directly and explicitlydistinguishing embodiments from discussed prior art, the embodimentnumbers are not approximates unless the word “about” is recited.

Although there are alternatives for various components, parameters,operating conditions, etc. set forth herein, that does not mean thatthose alternatives are necessarily equivalent and/or perform equallywell. Nor does it mean that the alternatives are listed in a preferredorder unless stated otherwise.

Definitions of common terms in chemistry may be found in Richard J.Lewis, Sr. (ed.), Hawley's Condensed Chemical Dictionary, published byJohn Wiley & Sons, Inc., 2016 (ISBN 978-1-118-13515-0).

In order to facilitate review of the various embodiments of thedisclosure, the following explanations of specific terms are provided:

Active salt: As used herein, the term “active salt” refers to a saltthat significantly participates in electrochemical processes ofelectrochemical devices. In the case of batteries, it refers to chargeand discharge processes contributing to the energy conversions thatultimately enable the battery to deliver/store energy. As used herein,the term “active salt” refers to a salt that constitutes at least 5% ofthe redox active materials participating in redox reactions duringbattery cycling after initial charging.

Annealing: A process in which a material is heated to a specifiedtemperature for a specified period of time and then gradually cooled.The annealing process may remove internal strains from previousoperations, and can eliminate distortions and imperfections to produce astronger and more uniform material.

Anode: An electrode through which electric charge flows into a polarizedelectrical device. From an electrochemical point of view,negatively-charged anions move toward the anode and/orpositively-charged cations move away from it to balance the electronsleaving via external circuitry.

Areal capacity or specific areal capacity is the capacity per unit areaof the electrode (or active material) surface, and is typicallyexpressed in united of mAh cm².

Capacity: The capacity of a battery is the amount of electrical charge abattery can deliver. The capacity is typically expressed in units ofmAh, or Ah, and indicates the maximum constant current a battery canproduce over a period of one hour. For example, a battery with acapacity of 100 mAh can deliver a current of 100 mA for one hour or acurrent of 5 mA for 20 hours.

Cathode: An electrode through which electric charge flows out of apolarized electrical device. From an electrochemical point of view,positively charged cations invariably move toward the cathode and/ornegatively charged anions move away from it to balance the electronsarriving from external circuitry.

Cell: As used herein, a cell refers to an electrochemical device usedfor generating a voltage or current from a chemical reaction, or thereverse in which a chemical reaction is induced by a current. Examplesinclude voltaic cells, electrolytic cells, and fuel cells, among others.A battery includes one or more cells. The terms “cell” and “battery” areused interchangeably when referring to a battery containing only onecell.

Coulombic efficiency (CE): The efficiency with which charges aretransferred in a system facilitating an electrochemical reaction. CE maybe defined as the amount of charge exiting the battery during thedischarge cycle divided by the amount of charge entering the batteryduring the charging cycle.

Current density: A term referring to the amount of current per unitarea. Current density is typically expressed in units of mA/cm².

Electrolyte: A substance containing free ions that behaves as anelectrically conductive medium. Electrolytes generally comprise ions ina solution, but molten electrolytes and solid electrolytes also areknown.

Microparticle: As used herein, the term “microparticle” refers to aparticle with a size measured in microns, such as a particle with adiameter of 1-100 μm.

Nanoparticle: As used herein, the term “nanoparticle” particle that hasa size measured in nanometers, such as a particle with a diameter of1-100 nm.

Pouch cell: A pouch cell is a battery completely, or substantiallycompletely, encased in a flexible outer covering, e.g., a heat-sealablefoil, a fabric, or a polymer membrane. The term “flexible” means thatthe outer covering is easy to bend without breaking; accordingly, theouter covering can be wrapped around the battery components. Because apouch cell lacks an outer hard shell, it is flexible and weighs lessthan conventional batteries.

Precursor: A precursor participates in a chemical reaction to formanother compound. As used herein, the term “precursor” refers tometal-containing compounds used to prepare lithium nickel manganesecobalt oxide and metal-doped lithium nickel manganese cobalt oxide.

Separator: A battery separator is a porous sheet or film placed betweenthe anode and cathode. It prevents physical contact between the anodeand cathode while facilitating ionic transport.

Solid state: Composed of solid components. As defined herein, asolid-state synthesis proceeds with solid components directly withoutusing sintering agents.

Specific capacity: A term that refers to capacity per unit of mass.Specific capacity may be expressed in units of mAh/g, and often isexpressed as mAh/g carbon when referring to a carbon-based electrode inLi/air batteries.

Specific energy: A term that refers to energy per unit of mass. Specificenergy is commonly expressed in units of Wh/kg or J/kg.

II. Synthesis of Crystalline Oxide Materials

Embodiments of methods for making monocrystalline lithium nickelmanganese cobalt oxide (NMC) and metal-doped lithium nickel manganesecobalt oxide are disclosed. In some embodiments, the monocrystallinelithium nickel manganese cobalt oxide has a formulaLiNi_(X)Mn_(y)M_(z)Co_(1-x-y-z)O₂, where M represents one or more dopantmetals, x≥0.6, 0.02≤y<0.2, 0≤z≤0.05, and x+y+z≤1.0. More particularly,0.62≤x+y+z≤1.0. In certain embodiments, z is 0, and the monocrystallinelithium nickel manganese cobalt oxide has a formulaLiNi_(X)Mn_(y)Co_(1-x-y)O₂, where x≥0.6, 0.02≤y<0.2, and x+y≤1.0. Moreparticularly, 0.62≤x+y≤1.0. In some embodiments, x=0.65-0.99,y=0.01-0.2, z=0-0.02, and x+y+z=0.66-1.0. In certain embodiments,x=0.65-0.9, y=0.05-0.2, z=0-0.02, and x+y+z=0.7-0.95. In some examples,x is 0.7-0.9, such as 0.75-0.9 or 0.8-0.9; y is 0.05-0.15, such as0.05-0.14 or 0.05-0.1; z is 0-0.02; and x+y+z is 0.8-0.98, such as0.8-0.95.

When the monocrystalline lithium nickel manganese cobalt oxide is doped,the general formula is LiNi_(X)Mn_(y)M_(z)Co_(1-x-y-z)O₂, where Mrepresents one or more dopant metals. In some embodiments, M representstwo or more dopant metals. Thus, M_(z) may refer collectively toM1_(z1)+M2_(z2)+M3_(z3) . . . +Mp_(zp), where M1, M2, M3, etc. representthe dopant metals, and z1+z2+z3 . . . +zp=z. Suitable dopant metalsinclude, but are not limited to, Mg, Ti, Al, Zn, Fe (e.g., Fe³⁺), Zr, Sn(e.g., Sn⁴⁺), Sc, V, Cr, Fe, Cu, Ga, Y, Nb, Mo, Ru, Ta, W, Ir, andcombinations thereof.

The lithium nickel manganese cobalt oxide crystals prepared byembodiments of the disclosed methods are microparticles. In someembodiments, the single crystals have a mean particle size of 1-5 μm,such as 1-4 μm or 1-3 μm. This feature is in stark contrast totraditional NMC comprising primary nanoparticles particles aggregatedinto secondary polycrystalline microparticles.

A. Hydroxide Precursor Synthesis

In any the foregoing or following embodiments, the synthesis may beginwith solid precursors comprising hydroxides of nickel, manganese, andcobalt. In some embodiments, the synthesis may further include solidhydroxide precursors of one or more dopant metals, e.g., hydroxides ofMg, Ti, Al, Zn, Fe, Zr, Sn, or any combination thereof. In someembodiments, the hydroxide precursor comprisesNi_(X)Mn_(y)M_(z)Co_(1-x-y-z)(OH)₂, where M represents one or moredopant metals, x≥0.6, 0.01≤y<0.2, z≤0.05, and x+y+z≤1.0. Moreparticularly, 0.62≤x+y+z≤1.0. In some embodiments, x=0.65-0.99,y=0.01-0.2, z=0-0.02, and x+y+z=0.66-1.0. In an independent embodiment,x=0.65-0.95, y=0.01-0.2, z=0-0.02, and x+y+z=0.66-0.98. In anotherindependent embodiment, x=0.65-0.9, y=0.05-0.2, z=0-0.02, andx+y+z=0.7-0.95. In some examples, x is 0.7-0.9, such as 0.75-0.9 or0.8-0.9; y is 0.05-0.15, such as 0.05-0.14 or 0.05-0.1; z is 0-0.02; andx+y+z is 0.8-0.98, such as 0.8-0.95.

In any the foregoing or following embodiments, the method ofsynthesizing monocrystalline lithium nickel manganese cobalt oxide(including doped variants), includes synthesizing the hydroxideprecursors. In some embodiments (FIG. 1 ), the hydroxide precursors aresynthesized by preparing a 1.5 M to 2.5 M solution comprising metalsalts in water (101), the metal salts comprising a nickel salt, amanganese salt, a cobalt salt, and optionally one or more dopant metalsalts; combining the solution comprising metal salts in water withaqueous NH₃ and aqueous NaOH or KOH to provide a combined solutionhaving a pH of 10.5-12 (102), aging the solution for 5-48 hours toco-precipitate hydroxides of nickel, manganese; and cobalt to providethe solid hydroxide precursor (103); and drying the solid hydroxideprecursor (104). In any of the foregoing or following embodiments, themetal salts may include a nickel (II) salt, a manganese (II) salt, and acobalt (II) salt (if x+y+z<1).

The solution comprising metal salts in water has a concentration of1.5-2.5 M, wherein 1.5 M to 2.5 M is a total concentration of all saltsin the water. In some embodiments, the concentration is 1.7 M to 2.3 M,1.8 M to 2.2 M, or 1.9 M to 2.1 M. In any of the foregoing or followingembodiments, the salts may be sulfates, nitrates, chlorides, acetates,or a combination thereof. In one embodiment, the salts are sulfates. Inanother embodiment, the salts are nitrates. The concentration of eachmetal salt is selected based on a desired amount of the metal in thefinal product. For example, when a hydroxide precursor comprisingNi_(0.76)Mn_(0.14)Co_(0.1)(OH)₂ is prepared, nickel, manganese, andcobalt salts are combined in a Ni:Mn:Co molar ratio of 0.76:0.14:0.1.Similarly, if a hydroxide precursor comprisingNi_(0.76)Mn_(0.12)Co_(0.1)Mg_(0.01)Ti_(0.01)(OH)₂ is prepared, nickel,manganese, cobalt, magnesium, and titanium salts are combined in aNi:Mn:Co:Mg:Ti molar ratio of 0.76:0.12:0.01:0.01.

In any of the foregoing or following embodiments, combining the solutioncomprising metal salts in water with aqueous NH₃ and aqueous NaOH or KOHto provide a pH of 10.5-12 may comprise preparing an aqueous NH₃solution comprising 0.5 wt % to 1 wt % or 0.2-0.5 M NH₃ in water;preheating the aqueous NH₃ solution to 25° C. to 80° C.; adding themetal salt solution, additional concentrated aqueous ammonia (e.g., 25wt % to 35 wt % or 13 M to 18 M NH₃—H₂O), and aqueous NaOH or KOH toprovide a pH of 10.5-12 and a final metal salt concentration of 0.1 M to3 M. In some embodiments, the aqueous NH₃ solution is preheated to 30°C. to 75° C., such as 35° C. to 70° C. 1-40° C. to 60° C., or 45° C. to55° C. In some embodiments, the final metal salt concentration is 0.1 Mto 2 M, 0.1 M to 1 M, or 0.2 M to 0.8 M. In some embodiments, the metalsalt solution and additional concentrated ammonia are added at the sametime at a volumetric ratio 2-4 parts metal salt solution to one partconcentrated ammonia solution. The aqueous NH₃ solution may be stirredcontinuously as the metal salt solution and concentrated ammoniasolution are added. In certain examples, the metal salt solution isadded at a rate of 3 mL/minute, and the concentrated ammonia is added ata rate of 1 mL/minute. Sufficient aqueous NaOH or KOH is added toprovide the combined solution with a pH of 10.5-12, such as a pH of11-11.5. In some embodiments, the aqueous NaOH or KOH has aconcentration of 6 M to 10 M. In any of the foregoing or followingembodiments, the combined solution may be aged for 5-48 hours at atemperature of 25° C. to 80° C. to co-precipitate hydroxides of themetals (Ni, Mn, Co, and any dopant metals), thereby producing thehydroxide precursor. In some embodiments, the combined solution isstirred continuously while aging. In certain embodiments, the combinedsolution is aged for 10 hours to 48 hours, 15 hours to 45 hours, 20hours to 40 hours, or 25 hours to 35 hours. In some embodiments, thetemperature is 30° C. to 75° C., such as 35° C. to 70° C. 1-40° C. to60° C., or 45° C. to 55° C. In some examples, the combined solution wasaged for 30 hours at 50° C. with continuous stirring.

In any of the foregoing or following embodiments, the hydroxideprecursor may be collected by any suitable method. In some embodiments,the aged combined solution is filtered to collect the co-precipitatedhydroxides. The collected hydroxide precursor may be washed, e.g., withdeionized water, to remove impurities, such as ammonia, residual NaOH orKOH, and/or soluble sulfate and/or nitrate salts. The hydroxideprecursor is then dried. In some embodiments, the hydroxide precursor isdried at a temperature of 80° C. to 120° C., such as 90° C. to 110° C.,for a period of 5 hours to 20 hours, such as 10 hours to 15 hours.

Advantageously, the low concentration, 1.5 M to 2.5 M, of the metal saltsolution facilitates formation of small hydroxide precursor particles.In any of the foregoing embodiments, embodiments, the hydroxideprecursor particles may have a mean size of 0.5 μm to 10 μm. In someembodiments, the hydroxide precursor particles have a mean size of 0.5μm to 7.5 μm, 0.5 μm to 5 μm, or 0.5 μm to 2.5 μm.

B. Solid-State Method

In some embodiments, monocrystalline lithium nickel manganese cobaltoxide (or a doped variant thereof) is synthesized by a solid-statemethod. With reference to FIG. 2 , in some embodiments, the solid-statemethod comprises heating a solid hydroxide precursor comprisingNi_(X)Mn_(y)M_(z)Co_(1-x-y-z)(OH)₂ at a temperature T_(S1) in anoxygen-containing atmosphere for an effective period of time t₁ toconvert the solid hydroxide precursor to a solid oxide precursor (201);combining the solid oxide precursor with a molar excess of a lithiumcompound (202); heating the solid oxide precursor and the lithiumcompound at a temperature T_(S2) for an effective period of time t₂ toproduce a first product (203); cooling the first product to ambienttemperature (204); reducing a mean particle size of the first product to0.1 μm to 10 μm (205); heating the first product having the reduced meanparticle size at a temperature T_(S3) for an effective period of time t₃to produce a second product (206); cooling the second product to ambienttemperature (207); reducing a mean particle size of the second productto 0.1 μm to 10 μm (208); and heating the second product having thereduced mean particle size at a temperature T_(S4) for an effectiveperiod of time t₄ to produce monocrystalline lithium nickel manganesecobalt oxide having a formula LiNi_(X)Mn_(y)M_(z)Co_(1-x-y-z)O₂ (209).In the foregoing formulas, M represents one or more dopant metals,x≥0.6, 0.01≤y<0.2, z≤0.05, and x+y+z≤1.0. More particularly,0.62≤x+y+z≤1.0. In some embodiments, x=0.65-0.99, y=0.01-0.2, z=0-0.02,and x+y+z=0.7-1.0. In an independent embodiment, x=0.65-0.95,y=0.01-0.2, z=0-0.02, and x+y+z=0.7-0.98. In another independentembodiment, x=0.65-0.9, y=0.05-0.2, z=0-0.02, and x+y+z=0.7-0.95. Insome examples, x=0.7-0.9, y=0.05-0.15, z=0-0.02, and x+y+z=0.7-0.95. Inone embodiment, x is 0.76, y is 0.14, and z is 0. In an independentembodiment, x is 0.76, y is 0.12, and z is 0.02. In another independentembodiment, x is 0.8, y is 0.1, and z is 0. In still another independentembodiment, x is 0.9, y is 0.05, and z is 0.

In any of the foregoing or following embodiments, the temperature T_(S1)may be 400° C. to 1000° C. and/or the effective period of time t₁ may be1 hour to 30 hours. In some embodiments, the temperature T_(S1) is 500°C. to 1000° C., 600° C. to 1000° C., 800° C. to 1000° C., or 850° C. to950° C. In certain examples, the temperature T_(S1) was 900° C.Advantageously, the temperature T_(S1) is below a melting point of thehydroxide precursor. In any of the foregoing or following embodiments,the temperature may be increased to the temperature T_(S1) at a rampingrate of 1° C./minute to 300° C./minute, such as a ramping rate of 1°C./minute to 200° C./minute, 1° C./minute to 100° C./minute, 1°C./minute to 50° C./minute, 5° C./minute to 25° C./minute, or 5°C./minute to 15° C./minute. In one example, the ramping rate was 10°C./minute. The temperature T_(S1) is then maintained for the effectiveperiod of time t₁. In some embodiments, the effective period of time t₁is 5 hours to 25 hours, 10 hours to 20 hours, or 12 hours to 18 hours.In certain examples, the effective period of time t₁ was 15 hours. Inany of the foregoing or following embodiments, the oxygen-containingatmosphere may be pure oxygen or air. As used herein, “pure oxygen”means at least 95 mol % oxygen. In any of the foregoing or followingembodiments, at a majority or all of the solid hydroxide precursor maybe converted to the solid oxide precursor. In some embodiments, 90 wt %to 100 wt %, such as 95 wt % to 100 wt %, 97 wt % to 100 wt %, 98 wt %to 100 wt %, or 99 wt % to 100 wt % of the solid hydroxide precursor isconverted to the solid oxide precursor. In certain embodiments, all ofthe solid hydroxide precursor is converted to the solid oxide precursor.

The solid oxide precursor is combined with a molar excess of a Licompound. In any of the foregoing or following embodiments, the Licompound may comprise lithium hydroxide, lithium carbonate, lithiumnitrate, lithium oxide, lithium peroxide, lithium acetate, lithiumoxalate or any combination thereof. In some embodiments, the Li compoundcomprises lithium hydroxide. The LiOH may be anhydrous or a hydratedsalt, e.g., LiOH.H₂O. In any of the foregoing or following embodiments,the Li compound may have a mean particle size of 10 μm to 100 μm. In anyof the foregoing or following embodiments, the solid oxide precursor andthe lithium compound may be combined in a Li:solid oxide precursor molarratio of 0.8:1 to 3:1, such as a molar ratio of 0.9:1 to 3:1, 1:05:1 to2:1, 1:05:1 to 1.5:1, 1.1:1 to 1.4:1 or 1.1:1 to 1.2:1. The mixture ofsolid oxide precursor and the Li compound is subjected to a series ofthree annealing processes to form a first product, a second product, andthe LiNi_(X)Mn_(y)M_(z)Co_(1-x-y-z)O₂.

The mixture of solid oxide precursor and the Li compound is heated at atemperature T_(S2) for an effective period of time t₂ to produce a firstproduct. In any of the foregoing or following embodiments, thetemperature T_(S2) may be 400° C. to 1000° C. and/or the effectiveperiod of time t₂ may be 1 hour to 30 hours. In some embodiments, thetemperature T_(S2) is 400° C. to 800° C., 400° C. to 600° C., or 450° C.to 550° C. Advantageously the temperature T_(S2) is less than a meltingor vaporization temperature of the oxide precursor and lithium compound.In certain examples, the temperature T_(S2) was 500° C. In someembodiments, the effective period of time h is 1 hour to 5 hours, 1 hourto 20 hours, 1 hours to 10 hours, or 2 hours to 6 hours. In certainexamples, the effective period of time t₂ was 5 hours.

The first product is cooled to ambient temperature and a mean particlesize of the first product is reduced to 0.1 μm to 10 μm. In someembodiments, the mean particle size is reduced to 0.2 μm to 10 μm, 0.5μm to 10 μm, or 1 μm to 10 μm. In any of the foregoing or followingembodiments, cooling the first product to ambient temperature maycomprise cooling the first product to 20° C. to 30° C., such as to 20°C. to 25° C. In any of the foregoing or following embodiments, reducinga mean particle size of the first product to 0.1 μm to 10 μm maycomprise grinding or milling the first product to achieve the desiredparticle size.

The first product having the reduced mean particle size is heated at atemperature T_(S3) for an effective period of time t₃ to produce asecond product. In any of the foregoing or following embodiments, thetemperature T_(S3) may be 600° C. to 1000° C. and/or the effectiveperiod of time t₃ may be 1-30 hours. In some embodiments, thetemperature T_(S3) is 700° C. to 1000° C., 700° C. to 900° C., or 750°C. to 850° C. In certain examples, the temperature T_(S3) was 800° C. Insome embodiments, the effective period of time t₃ is 1-25 hours, 1-20hours, 1-10 hours, or 2-6 hours. In certain examples, the effectiveperiod of time t₃ was 5 hours.

The second product is cooled to ambient temperature and a mean particlesize of the second product is reduced to 0.1 μm to 10 μm. In someembodiments, the mean particle size is reduced to 0.2 μm to 10 μm, 0.5μm to 10 μm, or 1 μm to 10 μm. In any of the foregoing or followingembodiments, cooling the second product to ambient temperature maycomprise cooling the second product to 20° C. to 30° C., such as to 20°C. to 25° C. In any of the foregoing or following embodiments, reducinga mean particle size of the second product to 0.1 μm to 10 μm maycomprise grinding or milling the second product to achieve the desiredparticle size.

The second product having the reduced mean particle size is heated at atemperature T_(S4) for an effective period of time t₄ to producemonocrystalline lithium nickel manganese cobalt oxide having a formulaLiNi_(X)Mn_(y)M_(z)Co_(1-x-y-z)O₂. In any of the foregoing or followingembodiments, the temperature T_(S4) may be 500° C. to 1000° C. and/orthe effective period of time t₄ may be 1-30 hours. In some embodiments,the temperature T_(S4) is 600° C. to 1000° C., 700° C. to 1000° C., 700°C. to 900° C., or 750° C. to 850° C. In certain examples, thetemperature T_(S4) was 800° C. In some embodiments, the effective periodof time t₄ is 1 hour to 25 hours, 1 hour to 20 hours, 1 hour to 10hours, or 2 hours to 6 hours. In certain examples, the effective periodof time t₄ was 5 hours.

In any of the foregoing or following embodiments, the solid hydroxideprecursor may be prepared as discussed above. In any of the foregoing orfollowing embodiments, the solid hydroxide precursor may have a meanparticle size of 0.5-10 μm. In some embodiments, the hydroxide precursorparticles have a mean size of 0.5 μm to 7.5 μm, 0.5 μm to 5 μm, or 0.5μm to 2.5 μm. In any of the foregoing or following embodiments,monocrystalline lithium nickel manganese cobalt oxide may have a meanparticle size of 0.5 μm to 5 μm. In some embodiments, the solidhydroxide precursor has a mean particle size of 1 μm to 2 μm. In certainembodiments, the monocrystalline lithium nickel manganese cobalt oxidehas a mean particle size of 1 μm to 5 μm, or 1 μm to 3 μm. In any of theforegoing or following embodiments, the dopant metal(s) M may compriseMg, Ti, Al, Zn, Fe, Zr, Sn, Sc, V, Cr, Fe, Cu, Ga, Y, Nb, Mo, Ru, Ta, W,Ir, or any combination thereof.

C. Molten-Salt Method

In some embodiments, monocrystalline lithium nickel manganese cobaltoxide (or a doped variant thereof) is synthesized by a molten-saltmethod. With reference to FIG. 3 , in some embodiments, the molten-saltmethod comprises heating a solid hydroxide precursor comprisingNi_(X)Mn_(y)M_(z)Co_(1-x-y-z)(OH)₂ at a temperature T_(M1) in anoxygen-containing atmosphere for an effective period of time t₁ toconvert the solid hydroxide precursor to a solid oxide precursor (301);combining the solid oxide precursor with a molar excess of a lithiumcompound and a sintering agent to form a mixture (302); heating themixture in an oxygen-containing atmosphere at a temperature T_(M2) for aperiod of time t₂ (303); increasing the temperature to a temperatureT_(M3), where T_(M3)>T_(M2), and heating the mixture at the temperatureT_(M3) for a period of time t₃ to produce a first product and thesintering agent (304); cooling the first product and the sintering agentto ambient temperature (305); separating the sintering agent from thefirst product (306); drying the first product (307); and heating thefirst product in an oxygen-containing atmosphere at a temperature T_(M4)for an effective period of time t₄ to restore any lost oxygen in thelattices and produce monocrystalline lithium nickel manganese cobaltoxide having a formula LiNi_(X)Mn_(y)M_(z)Co_(1-x-y-z)O₂ (308). In theforegoing formulas, M represents one or more dopant metals, x≥0.6,0.01≤y<0.2, z≤0.05, and x+y+z≤1.0. More particularly, 0.62≤x+y+z≤1.0. Insome embodiments, x=0.65-0.99, y=0.01-0.2, z=0-0.02, and x+y+z=0.66-1.0.In an independent embodiment, x=0.65-0.95, y=0.01-0.2, z=0-0.02, andx+y+z=0.7-0.98. In another independent embodiment, x=0.65-0.9,y=0.05-0.2, z=0-0.02, and x+y+z=0.7-0.95. In some examples, x is0.7-0.9, such as 0.75-0.9 or 0.8-0.9; y is 0.05-0.15, such as 0.05-0.14or 0.05-0.1; z is 0-0.02; and x+y+z is 0.8-0.98, such as 0.8-0.95.

In any of the foregoing or following embodiments, the temperature T_(M1)may be 400° C. to 1000° C. and/or the effective period of time t₁ may be1 hour to 30 hours. In some embodiments, the temperature T_(M1) is 500°C. to 1000° C., 600° C. to 1000° C., 800° C. to 1000° C., or 850° C. to950° C. In certain examples, the temperature T_(M1) was 800° C., 900°C., or 1000° C. Advantageously, the temperature T_(M1) is below amelting point of the hydroxide precursor. In any of the foregoing orfollowing embodiments, the temperature may be increased to thetemperature T_(M1) at a ramping rate of 1° C./minute to 300° C./minute,such as a ramping rate of 1° C./minute to 200° C./minute, 1° C./minute100° C./minute, 1° C./minute 50° C./minute, 1° C./minute 25° C./minute,or 1° C./minute 15° C./minute. In one example, the ramping rate was 5°C./minute. The temperature T_(M1) is then maintained for the effectiveperiod of time t₁. In some embodiments, the effective period of time t₁is 5 hours to 25 hours, 10 hours to 20 hours, or 12 hours to 18 hours.In certain examples, the effective period of time t₁ was 15 hours. Inany of the foregoing or following embodiments, the oxygen-containingatmosphere may be air or pure oxygen. In some embodiments, theoxygen-containing atmosphere is air. In any of the foregoing orfollowing embodiments, at a majority or all of the solid hydroxideprecursor may be converted to the solid oxide precursor. In someembodiments, 90 wt % to 100 wt %, such as 95 wt % to 100 wt %, 97 wt %to 100 wt %, 98 wt % to 100 wt %, or 99 wt % to 100 wt % of the solidhydroxide precursor is converted to the solid oxide precursor. Incertain embodiments, all of the solid hydroxide precursor is convertedto the solid oxide precursor.

The solid oxide precursor is combined with a molar excess of a Licompound and a sintering agent to form a mixture. In any of theforegoing or following embodiments, the Li compound may comprise lithiumhydroxide, lithium carbonate, lithium nitrate, lithium oxide, lithiumperoxide, or any combination thereof. In any of the foregoing orfollowing embodiments, the Li compound may have a mean particle size of10 μm to 100 μm. In some embodiments, the Li compound comprises lithiumoxide (Li₂O). In any of the foregoing or following embodiments, thesolid oxide precursor and the lithium compound may be combined in aLi:solid oxide precursor molar ratio of 1:1 to 5:1, such as a molarratio of 1:1 to 4:1, 1:1 to 3:1, 1:1 to 2:1, 1:1 to 1.5:1, 1.1:1 to1.4:1, or 1.1:1 to 1.2:1. In any of the foregoing or followingembodiments, the sintering agent may be NaCl or KCl. In someembodiments, the sintering agent is NaCl. NaCl may reduce the sinteringtemperature and/or time. In any of the foregoing or followingembodiments, a weight ratio of the sintering agent to the combined solidoxide precursor and lithium compound may be 0.2:1 to 1:0.2, such asweight ratio of 0.3:1 to 1:0.3, 0.4:1 to 1:0.4, 0.5:1 to 1:0.5, 0.6:1 to1:0.6, 0.7:1 to 1:0.7, 0.8:1 to 1:0.8, 0.85:1 to 1:0.85, or 0.9:1 to1:0.9. In certain examples, the weight ratio was 1:1.

The mixture is heated in an oxygen-containing atmosphere at atemperature T_(M2) for a period of time t₂. In any of the foregoing orfollowing embodiments, the temperature may be increased to thetemperature T_(M2) at a ramping rate of 1° C./minute to 300° C./minute,such as a ramping rate of 1° C./minute to 200° C./minute, 1° C./minuteto 100° C./minute, 1° C./minute to 50° C./minute, 5° C./minute to 25°C./minute, or 5° C./minute to 15° C./minute. In one example, the rampingrate was 10° C./minute. The temperature T_(M2) is then maintained forthe effective period of time t₂. In any of the foregoing or followingembodiments, the temperature T_(M2) may be 400-1000° C. and/or theeffective period of time t₂ may be 1-30 hours. In some embodiments, thetemperature T_(M2) is 500° C. to 1000° C., 600° C. to 1000° C., 700° C.to 900° C., or 750° C. to 850° C. In certain examples, the temperatureT_(M2) was 800° C. In some embodiments, the effective period of time t₂is 1 hour to 25 hours, 5 hours to 20 hours, or 5 hours to 15 hours. Incertain examples, the effective period of time t₂ was 10 hours. In anyof the foregoing or following embodiments, the oxygen-containingatmosphere may be air or pure oxygen. In some embodiments, theoxygen-containing atmosphere is pure oxygen.

The mixture then is heated at a temperature T_(M3) for a period of timet₃ to produce a first product and the sintering agent. The temperatureT_(M3) is greater than the temperature T_(M2). In any of the foregoingor following embodiments, the temperature T_(M3) may be 600° C. to 1000°C. and/or the effective period of time t₃ may be 1-30 hours. In someembodiments, the temperature T_(M3) is 700° C. to 1000° C., 800° C. to1000° C., or 850° C. to 950° C. In certain examples, the temperatureT_(M3) was 900° C. In some embodiments, the effective period of time t₃is 1 hour to 25 hours, 1 hour to 20 hours, 1 hour to 10 hours, or 2hours to 6 hours. In certain examples, the effective period of time t₃was 5 hours.

The first product and sintering agent are cooled to ambient temperature.In any of the foregoing or following embodiments, cooling the firstproduct to ambient temperature may comprise cooling the first product to20° C. to 30° C., such as to 20° C. to 25° C. In some embodiments, amean particle size of the first product is reduced to 0.1 μm to 10 μm.In any of the foregoing or following embodiments, reducing a meanparticle size of the first product to 0.1 μm to 10 μm may comprisegrinding the first product to achieve the desired particle size.

The sintering agent is separated from the first product. In any of theforegoing or following embodiments, separating the sintering agent maycomprise washing the sintering agent and the first product with asolvent in which the sintering agent is soluble and the first product isinsoluble or substantially insoluble (e.g., less than 5 wt % of thefirst product is soluble in the solvent). In some embodiments, thesolvent is water. In certain embodiments, washing the sintering agentand first product comprises stirring the ground sintering agent andfirst product in water and/or ultrasonicating the ground sintering agentand first product in the water. The resulting solution may be filteredto collect the first product. The first product then is dried to removewater. In any of the foregoing or following embodiments, drying thefirst product may comprise heating the first product at a temperatureeffective to evaporate the solvent for a time effective to remove thesolvent, e.g., to remove at least 80 wt %, at least 90%, at least 95 wt%, at least 97 wt %, or at least 99 wt % of the solvent. In someembodiments, the solvent is water and the temperature is 60° C. to 95°C., such as 70° C. to 90° C. In certain embodiments, the first productmay be heated under a reduced pressure to facilitate solvent removal. Inany of the foregoing or following embodiments, the time may be from 1-10hours, such as from 1-5 hours or from 1-3 hours. In some examples, thefirst product is heated under vacuum at 80° C. for 2 hours.

The first product is heated in an oxygen-containing atmosphere at atemperature T_(M4) for an effective period of time t₄ and producemonocrystalline lithium nickel manganese cobalt oxide having a formulaLiNi_(X)Mn_(y)M_(z)Co_(1-x-y-z)O₂. In any of the foregoing or followingembodiments, the temperature T_(M4) may be 500° C. to 1000° C. and/orthe effective period of time t₄ may be 1 hour to 30 hours. In someembodiments, the temperature T_(M4) is 500° C. to 800° C., 500° C. to700° C., or 550° C. to 650° C. In certain examples, the temperatureT_(M4) was 580° C. In some embodiments, the effective period of time t₄is 1 hour to 25 hours, 1 hour to 20 hours, 1 hour to 10 hours, or 2hours to 6 hours. In certain examples, the effective period of time t₄was 4 hours. In any of the foregoing or following embodiments, theoxygen-containing atmosphere may be air or pure oxygen. In someembodiments, the oxygen-containing atmosphere is pure oxygen.

In any of the foregoing or following embodiments, the hydroxideprecursor may be prepared as discussed above. In any of the foregoing orfollowing embodiments, the solid hydroxide precursor may have a meanparticle size of 0.5 μm to 10 μm. In some embodiments, the hydroxideprecursor particles have a mean size of 0.5 μm to 7.5 μm, 0.5 μm to 5μm, or 0.5 μm to 2.5 μm. In any of the foregoing or followingembodiments, monocrystalline lithium nickel manganese cobalt oxide mayhave a mean particle size of 0.5 μm to 5 μm. In some embodiments, thesolid hydroxide precursor has a mean particle size of 1 μm to 2 μm. Incertain embodiments, the monocrystalline lithium nickel manganese cobaltoxide has a mean particle size of 1 μm to 5 μm, or 1 μm to 3 μm. In anyof the foregoing or following embodiments, the dopant metal(s) M maycomprise Mg, Ti, Al, Zn, Fe, Zr, Sn, Sc, V, Cr, Fe, Cu, Ga, Y, Nb, Mo,Ru, Ta, W, Ir, or any combination thereof.

D. Flash-Sintering Method

In some embodiments, monocrystalline lithium nickel manganese cobaltoxide (or a doped variant thereof) is synthesized by a flash-sinteringmethod. With reference to FIG. 4 , in some embodiments, theflash-sintering method comprises combining a solid hydroxide precursorcomprising Ni_(X)Mn_(y)M_(z)Co_(1-x-y-z)(OH)₂ with a molar excess of alithium compound to form a hydroxide mixture (401); heating thehydroxide mixture in an oxygen-containing atmosphere at a temperatureT_(F1) for an effective period of time t₁ to form an oxide mixturecomprising oxides of nickel, manganese, cobalt, lithium, and, ifpresent, the one or more dopant metals, or a combination thereof (402);increasing the temperature to a temperature T_(F2) at a rate of ≥10°C./min (403); and heating the oxide mixture in an oxygen-containingatmosphere at the temperature T_(F2) for an effective period of time t₂to form monocrystalline lithium nickel manganese cobalt oxide having aformula LiNi_(X)Mn_(y)M_(z)Co_(1-x-y-z)O₂ (404). In the foregoingformulas, M represents one or more dopant metals, x≥0.6, 0.01≤y<0.2,z≤0.05, and x+y+z≤1.0. More particularly, 0.62≤x+y+z≤1.0. In someembodiments, x=0.65-0.99, y=0.01-0.2, z=0-0.02, and x+y+z=0.7-1.0. In anindependent embodiment, x=0.65-0.95, y=0.01-0.2, z=0-0.02, andx+y+z=0.7-0.98. In another independent embodiment, x=0.65-0.9,y=0.05-0.2, z=0-0.02, and x+y+z=0.7-0.95. In some examples, x is0.7-0.9, such as 0.75-0.9 or 0.8-0.9; y is 0.05-0.15, such as 0.05-0.14or 0.05-0.1; z is 0-0.02; and x+y+z is 0.8-0.98, such as 0.8-0.95.

The solid hydroxide precursor is combined with a molar excess of a Licompound to form a hydroxide mixture. In any of the foregoing orfollowing embodiments, the Li compound may comprise lithium hydroxide,lithium carbonate, lithium nitrate, lithium oxide, lithium peroxide, orany combination thereof. In any of the foregoing or followingembodiments, the Li compound may have a mean particle size of 10 μm to100 μm. In some embodiments, the Li compound comprises lithiumhydroxide. The LiOH may be anhydrous or a hydrated salt, e.g., LiOH.H₂O.In any of the foregoing or following embodiments, the solid hydroxideprecursor and the lithium compound may be combined in a Li:solidhydroxide precursor molar ratio of 0.8:1 to 3:1, such as a molar ratioof 0.9:1 to 3:1, 0.9:1 to 2:1, 0.9:1 to 1.5:1, 1:1 to 1.5:1, 1.1:1 to1.4:1, or 1.1:1 to 1.2:1.

The hydroxide mixture is heated in an oxygen-containing atmosphere at atemperature T_(F1) for an effective period of time t₁ to form an oxidemixture comprising oxides of nickel, manganese, cobalt, lithium, and, ifpresent, the one or more dopant metals, or a combination thereof. Insome embodiments, the hydroxide mixture is heated at the temperatureT_(F1) in an absence of a sintering agent. In any of the foregoing orfollowing embodiments, the temperature T_(F1) may be 400° C. to 1000° C.and/or the effective period of time t₁ may be 1 hour to 30 hours. Insome embodiments, the temperature T_(F1) is 400° C. to 900° C., 400° C.to 800° C., 400° C. to 600° C., or 450° C. to 550° C. In certainexamples, the temperature T_(F1) was 480° C. In any of the foregoing orfollowing embodiments, the effective period of time t₁ is 1 hour tohours In some embodiments, the effective period of time t₁ is 1 hour to25 hours, 1 hour to 20 hours, 1 hour to 15 hours, or 1 hour to 10 hours.In certain examples, the period of time t₁ was 5 hours. In any of theforegoing or following embodiments, the oxygen-containing atmosphere maybe air or pure oxygen. In some embodiments, the oxygen-containingatmosphere is pure oxygen. In any of the foregoing or followingembodiments, a portion or all of the hydroxide mixture is converted toan oxide mixture. In some embodiments, at least 25 wt %, at least 50 wt%, at least 75 wt %, or at least 90 wt % of the hydroxide mixture isconverted to an oxide mixture. In certain embodiments, 25-100 wt %,50-100 wt %, 75-100 wt %, 90-100 wt %, or 95-100 wt % of the hydroxidemixture is converted to an oxide mixture.

The temperature is then increased to a temperature T_(F2) at a rate of≥10° C./minute. In any of the foregoing or following embodiments, theramping rate may be from 10° C./minute to 3000° C./minute (50°C./second). In some embodiments, the ramping rate is from 10° C./minuteto 2000° C./minute, such as 10° C./minute to 1000° C./minute, 10°C./minute to 500° C./minute, 10° C./minute to 250° C./minute, or 10°C./minute to 100° C./minute. In certain examples, the ramping rate was10-20° C./minute. In any of the foregoing or following embodiments, thetemperature T_(F2) may be 600° C. to 1000° C. In some embodiments, thetemperature T_(F2) is 700° C. to 800° C. or 750° C. to 850° C. In someexamples, the temperature T_(F2) was 800° C.

The oxide mixture is heated in an oxygen-containing atmosphere at thetemperature T_(F2) for an effective period of time t₂ to formmonocrystalline lithium nickel manganese cobalt oxide having a formulaLiNi_(X)Mn_(y)M_(z)Co_(1-x-y-z)O₂. In any of the foregoing or followingembodiments, the effective period of time t₂ may be 1 hour to 30 hours.In some embodiments, the effective period of time t₂ is 1 hour to 25hours, 1 hour to 20 hours, 5 hours to 20 hours, or 5 hours to 15 hours.In certain examples, the period of time t₂ was 10 hours. In any of theforegoing or following embodiments, the oxygen-containing atmospherecomprises pure oxygen or air. In some embodiments, the oxygen-containingatmosphere is pure oxygen.

In any of the foregoing or following embodiments, the hydroxideprecursor may be prepared as discussed above. In any of the foregoing orfollowing embodiments, the solid hydroxide precursor may have a meanparticle size of 0.5 μm to 10 μm. In some embodiments, the hydroxideprecursor particles have a mean size of 0.5 μm to 7.5 μm, 0.5 μm to 5μm, or 0.5 μm to 2.5 μm. In any of the foregoing or followingembodiments, monocrystalline lithium nickel manganese cobalt oxide mayhave a mean particle size of 0.5 μm to 5 μm. In some embodiments, thesolid hydroxide precursor has a mean particle size of 1 μm to 2 μm. Incertain embodiments, the monocrystalline lithium nickel manganese cobaltoxide has a mean particle size of 1 μm to 5 μm, or 1 μm to 3 μm. In anyof the foregoing or following embodiments, the dopant metal(s) M maycomprise Mg, Ti, Al, Zn, Fe, Zr, Sn, Sc, V, Cr, Fe, Cu, Ga, Y, Nb, Mo,Ru, Ta, W, Ir, or any combination thereof.

III. Cathodes and Lithium Ion Batteries

Monocrystalline lithium nickel manganese cobalt oxide (NMC), and dopedvariants thereof, made by embodiments of the disclosed methods may beused in cathodes, such as cathodes for lithium ion batteries. In someembodiments, a cathode comprises monocrystallineLiNi_(X)Mn_(y)M_(z)Co_(1-x-y-z)O₂ where M represents one or more dopantmetals, x≥0.6, 0.01≤y<0.2, z≤0.05, and x+y+z≤1.0. In some embodiments,x=0.65-0.99, y=0.01-0.2, z=0-0.02, and x+y+z=0.66-1.0. In an independentembodiment, x=0.65-0.95, y=0.01-0.2, z=0-0.02, and x+y+z=0.66-0.98. Inanother independent embodiment, x=0.65-0.9, y=0.05-0.2, z=0-0.02, andx+y+z=0.7-0.95. In some examples, x is 0.7-0.9, such as 0.75-0.9 or0.8-0.9; y is 0.05-0.15, such as 0.05-0.14 or 0.05-0.1; z is 0-0.02; andx+y+z is 0.8-0.98, such as 0.8-0.95.

In any of the foregoing or following embodiments, a mean particle sizeof the monocrystalline LiNi_(X)Mn_(y)M_(z)Co_(1-x-y-z)O₂ may be 0.5 μmto 5 μm, such as 1 μm to 5 μm, or 1 μm to 3 μm. In one embodiment, theNMC is LiNi_(0.76)Mn_(0.14)Co_(0.1)O₂. In an independent embodiment, theNMC is LiNi_(0.8)Mn_(0.1)Co_(0.1)O₂. In another independent embodiment,the NMC is LiNi_(0.9)Mn_(0.05)Co_(0.05)O₂. In still another independentembodiment, the NMC is LiNi_(0.76)Mn_(0.12)Co_(0.1)Mg_(0.01)Ti_(0.01)O₂.

In any of the foregoing or following embodiments, the cathode may have acapacity >180 mAh/g. In some embodiments, the cathode has acapacity >185 mAh/g, >190 mAh/g, or even >200 mAh/g. In any of theforegoing or following embodiments, the cathode may be operable at highvoltage, e.g., a voltage of >3.8 V. In some embodiments, the cathode isoperable at a voltage from 2-4.6 V, such as a voltage of 2-4.5 V or2-4.4 V. In any of the foregoing or following embodiments, the cathodemay have an NMC loading of 15-25 mg/cm², such as 18-24 mg/cm² (ca.3.5-4.5 mAh/cm²). In some embodiments, the coating weight on each sideof the cathode may be from 7.5-12.5 mg/cm², such as 9-12 mg/cm²,providing an areal capacity on each side of 3.5-4.5 mAh/cm².

In any of the foregoing or following embodiments, the cathode mayfurther comprise one or more inactive materials, such as binders and/oradditives (e.g., carbon). In some embodiments, the cathode may comprisefrom 0-10 wt %, such as 2-5 wt % inactive materials. Suitable bindersinclude, but are not limited to, polyvinyl alcohol, polyvinyl fluoride,ethylene oxide polymers, polyvinylpyrrolidone, polyurethane,polytetrafluoroethylene, polyvinylidene fluoride, polyethylene,polypropylene, styrene-butadiene rubber, epoxy resin, nylon, polyimideand the like. Suitable conductive additives include, but are not limitedto, carbon black, acetylene black, Ketjen black, carbon fibers (e.g.,vapor-grown carbon fiber), metal powders or fibers (e.g., Cu, Ni, Al),and conductive polymers (e.g., polyphenylene derivatives). In someembodiments, a slurry comprising the NMC and, optionally, inactivematerials is coated onto a support, such as aluminum foil. In certainembodiments, the coating may have a thickness of 50-80 μm on each side,such as a thickness of 60-70 μm. In any of the foregoing or followingembodiments, the cathode may have an electrode press density of 2.5-3.5g/cm³, such as 3 g/cm³.

In some embodiments, a lithium ion battery includes a cathode comprisingmonocrystalline NMC as disclosed herein, an anode, an electrolyte, andoptionally a separator. FIG. 5 is a schematic diagram of one exemplaryembodiment of a rechargeable battery 500 including a cathode 520 asdisclosed herein, a separator 530 which is infused with an electrolyte,and an anode 540. In some embodiments, the battery 500 also includes acathode current collector 510 and/or an anode current collector 550. Theelectrolyte may be any electrolyte that is compatible with the anode andsuitable for use in a lithium ion battery.

In any of the foregoing or following embodiments, the lithium ionbattery may be a pouch cell. FIG. 6 is a schematic side elevation viewof one embodiment of a simplified pouch cell 600. The pouch cell 600comprises an anode 610 comprising graphite material, an anode currentcollector 630, a cathode 640 comprising an NMC cathode material 650 asdisclosed herein and a cathode current collector 660, a separator 670,and a packaging material defining a pouch 680 enclosing the anode 610,cathode 640, and separator 670. The pouch 680 further encloses anelectrolyte (not shown). The anode current collector 630 has aprotruding tab 631 that extends external to the pouch 680, and thecathode current collector 660 has a protruding tab 661 that extendsexternal to the pouch 680. The pouch cell weight includes all componentsof the cell, i.e., anode, cathode, separator, electrolyte, and pouchmaterial. In some embodiments, the pouch cell has a ratio of anode(negative electrode) areal capacity to cathode (positive electrode)areal capacity—N/P ratio—of 0.02-5, 0.1-5, 0.5-5, or 1-5. In certainembodiments, the pouch cell has a ratio of electrolyte mass to cellcapacity—E/C ratio—of 1-6 g/Ah, such as 2-6 g/Ah or 2-4 g/Ah.

In any of the foregoing or following embodiments, the current collectorscan be a metal or another conductive material such as, but not limitedto, nickel (Ni), copper (Cu), aluminum (Al), iron (Fe), stainless steel,or conductive carbon materials. The current collector may be a foil, afoam, or a polymer substrate coated with a conductive material.Advantageously, the current collector is stable (i.e., does not corrodeor react) when in contact with the anode or cathode and the electrolytein an operating voltage window of the battery. The anode and cathodecurrent collectors may be omitted if the anode or cathode, respectively,are free standing, e.g., when the anode is a free-standing film, and/orwhen the cathode is a free-standing film. By “free-standing” is meantthat the film itself has sufficient structural integrity that the filmcan be positioned in the battery without a support material.

In any of the foregoing or following embodiments, the anode may be anyanode suitable for a lithium ion battery. In some embodiments, the anodeis lithium metal, graphite, an intercalation material, or a conversioncompound. The intercalation material or conversion compound may bedeposited onto a substrate (e.g., a current collector) or provided as afree-standing film, typically, including one or more binders and/orconductive additives. Suitable binders include, but are not limited to,polyvinyl alcohol, polyvinyl chloride, polyvinyl fluoride, ethyleneoxide polymers, polyvinylpyrrolidone, polyurethane,polytetrafluoroethylene, polyvinylidene fluoride, polyethylene,polypropylene, styrene-butadiene rubber, epoxy resin, nylon, polyimideand the like. Suitable conductive additives include, but are not limitedto, carbon black, acetylene black, Ketjen black, carbon fibers (e.g.,vapor-grown carbon fiber), metal powders or fibers (e.g., Cu, Ni, Al),and conductive polymers (e.g., polyphenylene derivatives). Exemplaryanodes for lithium batteries include, but are not limited to, lithiummetal, carbon-based anodes (e.g., graphite, silicon-based anodes (e.g.,porous silicon, carbon-coated porous silicon, carbon/siliconcarbide-coated porous silicon), Mo₆S₈, TiO₂, V₂O₅, Li₄Mn₅O₁₂, Li₄Ti₅O₁₂,C/S composites, and polyacrylonitrile (PAN)-sulfur composites. In someembodiments, the anode is lithium metal. In certain embodiments, theanode may have a lithium coating weight on each side of a currentcollector of 5-15 mg/cm², providing an areal capacity on each side of2-5.1 mAh/cm².

In any of the foregoing or following embodiments, the separator may beglass fiber, a porous polymer film (e.g., polyethylene- orpolypropylene-based material) with or without a ceramic coating, or acomposite (e.g., a porous film of inorganic particles and a binder). Oneexemplary polymeric separator is a Celgard® K1640 polyethylene (PE)membrane. Another exemplary polymeric separator is a Celgard® 2500polypropylene membrane. Another exemplary polymeric separator is aCelgard® 3501 surfactant-coated polypropylene membrane. The separatormay be infused with the electrolyte.

In any of the foregoing or following embodiments, the electrolyte maycomprise a lithium active salt and a solvent. In some embodiments, thelithium active salt comprises LiPF₆, LiAsF₆, LiBF₄, lithiumbis(fluorosulfonyl)imide (LiFSI), lithiumbis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(oxalato)borate(LiB(C₂O₄)₂, LiBOB), lithium difluoro(oxalato)borate (LiBF₂(C₂O₄),LiDFOB), lithium bis(pentafluoroethanesulfonyl)imide (LiN(SO₂CF₂CF₃)₂,LiBETI), lithium (fluorosulfonyl trifluoromethanesulfonyl)imide(LiN(SO₂F)(SO₂CF₃), LiFTFSI), lithium (fluorosulfonylpentafluoroethanesulfonyl)imide (LiN(SO₂F)N(SO₂CF₂CF₃), LiFBETI),lithium cyclo(tetrafluoroethylenedisulfonyl)imide (LiN(SO₂CF₂CF₂SO₂),LiCTFSI), lithium(trifluoromethanesulfonyl)(n-nonafluorobutanesulfonyl)imide(LiN(SO₂CF₃)(SO₂-n-C₄F₉), LiTNFSI), lithiumcyclo-hexafluoropropane-1,3-bis(sulfonyl)imide, or any combinationthereof. The solvent is any nonaqueous solvent suitable for use with thelithium active salt, lithium metal anode, and packaging material.Exemplary solvents include, but are not limited to, triethyl phosphate,trimethyl phosphate, tributyl phosphate, triphenyl phosphate,tris(2,2,2-trifluoroethyl) phosphate, bis(2,2,2-trifluoroethyl) methylphosphate; trimethyl phosphite, triphenyl phosphite,tris(2,2,2-trifluoroethyl) phosphite; dimethyl methylphosphonate,diethyl ethylphosphonate, diethyl phenylphosphonate,bis(2,2,2-trifluoroethyl) methylphosphonate; hexamethylphosphoramide;hexamethoxyphosphazene, hexafluorophosphazene, 1,2-dimethoxyethane(DME), 1,3-dioxolane (DOL), tetrahydrofuran (THF), allyl ether, dimethylcarbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC),ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate(VC), fluoroethylene carbonate (FEC), 4-vinyl-1,3-dioxolan-2-one (vinylethylene carbonate, VEC), 4-methylene-1,3-dioxolan-2-one (methyleneethylene carbonate, MEC), 4,5-dimethylene-1,3-dioxolan-2-one, dimethylsulfoxide (DMSO), dimethyl sulfone (DMS), ethyl methyl sulfone (EMS),ethyl vinyl sulfone (EVS), tetramethylene sulfone (i.e. sulfolane, TMS),trifluoromethyl ethyl sulfone (FMES), trifluoromethyl isopropyl sulfone(FMIS), trifluoropropyl methyl sulfone (FPMS), diethylene glycoldimethyl ether (diglyme), triethylene glycol dimethyl ether (triglyme),tetraethylene glycol dimethyl ether (tetraglyme), methyl butyrate, ethylpropionate, gamma-butyrolactone, acetonitrile (AN), succinonitrile (SN),adiponitrile, triallyl amine, triallyl cyanurate, triallyl isocyanurate,or any combination thereof. In some embodiments, the solvent comprises aflame retardant compound. The flame retardant compound may comprise theentire solvent. Alternatively, the solvent may comprise at least 5 wt %of the flame retardant compound in combination with one or moreadditional solvents and/or diluents. Exemplary flame retardant compoundsinclude, but are not limited to, triethyl phosphate, trimethylphosphate, tributyl phosphate, triphenyl phosphate,tris(2,2,2-trifluoroethyl) phosphate, bis(2,2,2-trifluoroethyl) methylphosphate; trimethyl phosphite, triphenyl phosphite,tris(2,2,2-trifluoroethyl) phosphite; dimethyl methylphosphonate,diethyl ethylphosphonate, diethyl phenylphosphonate,bis(2,2,2-trifluoroethyl) methylphosphonate; hexamethylphosphoramide;hexamethoxyphosphazene, hexafluorophosphazene, and combinations thereof.In some embodiments, the electrolyte has a lithium active saltconcentration of 0.5-8 M, such as a concentration of 1-8 M, 1-6 M, or1-5 M. In some examples, the electrolyte comprises LiPF₆ in a carbonatesolvent, such as 1.0 M LiPF₆ in EC/EMC.

In some embodiments, the electrolyte is a localized superconcentratedelectrolyte (LSE), also referred to as a localized high concentrationelectrolyte. A LSE includes an active salt, a solvent in which theactive salt is soluble, and a diluent, wherein the active salt has asolubility in the diluent at least 10 times less than a solubility ofthe active salt in the solvent. In an LSE, lithium ions remainassociated with solvent molecules after addition of the diluent. Theanions are also in proximity to, or associated with, the lithium ions.Thus, localized regions of solvent-cation-anion aggregates are formed.In contrast, the lithium ions and anions are not associated with thediluent molecules, which remain free in the solution. In an LSE, theelectrolyte as a whole is not a concentrated electrolyte, but there arelocalized regions of high concentration where the lithium cations areassociated with the solvent molecules. There are few to no free solventmolecules in the diluted electrolyte, thereby providing the benefits ofa superconcentrated electrolyte without the associated disadvantages.The solubility of the active salt in the solvent (in the absence ofdiluent) may be greater than 3 M, such as at least 4 M or at least 5 M.In some embodiments, the solubility and/or concentration of the activesalt in the solvent is of 3 M to 10 M, such as from 3 M to 8 M, from 4 Mto 8 M, or from 5 M to 8 M. However, in some embodiments, the molarconcentration of the active salt in the LSE as a whole is of 0.5 M to 3M, 0.5 M to 2 M, 0.75 M to 2 M, or 0.75 M to 1.5 M.

Exemplary salts and solvents for LSEs are those disclosed above. In someembodiments, the diluent comprises a fluoroalkyl ether (also referred toas a hydrofluoroether (HFE)), a fluorinated orthoformate, or acombination thereof. Exemplary diluents include, but are not limited to,1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE),bis(2,2,2-trifluoroethyl) ether (BTFE),1,1,2,2,-tetrafluoroethyl-2,2,2-trifluoroethyl ether (TFTFE),methoxynonafluorobutane (MOFB), ethoxynonafluorobutane (EOFB),tris(2,2,2-trifluoroethyl)orthoformate (TFEO),tris(hexafluoroisopropyl)orthoformate (THFiPO),tris(2,2-difluoroethyl)orthoformate (TDFEO), bis(2,2,2-trifluoroethyl)methyl orthoformate (BTFEMO),tris(2,2,3,3,3-pentafluoropropyl)orthoformate (TPFPO),tris(2,2,3,3-tetrafluoropropyl)orthoformate (TTPO), or any combinationthereof. In certain embodiments where the diluent and solvent areimmiscible, the electrolyte may further include a bridge solvent havinga different composition than the solvent and a different compositionthan the diluent, wherein the bridge solvent is miscible with thesolvent and with the diluent. Exemplary bridge solvents includeacetonitrile, dimethyl carbonate, diethyl carbonate, propylenecarbonate, dimethyl sulfoxide, 1,3-dioxolane, dimethoxyethane, diglyme(bis(2-methoxyethyl) ether), triglyme (triethylene glycol dimethylether), tetraglyme (tetraethylene glycol dimethyl ether), or anycombination thereof. Additional information regarding LSEs may be foundin US 2018/0254524 A1, US 2018/0251681 A1, and US 2019/148775 A1, eachof which is incorporated in its entirety herein by reference.

In any of the foregoing or following embodiments, the lithium ionbattery may have a cell energy density of 200 Wh/kg to 400 Wh/kg, suchas 200 Wh/kg to 350 Wh/kg, 250 Wh/kg to 300 Wh/kg, or 250 Wh/kg to 275Wh/kg. In any of the foregoing or following embodiments, the lithium ionbattery may have a first cycle capacity of 2 Ah to 5 Ah. In any of theforegoing or following embodiments, the lithium ion battery may beoperable at a rate of up to 3 C, such as a rate of 0.1 C to 3 C. In anyof the foregoing or following embodiments, the lithium ion battery maydemonstrate an average coulombic efficiency of at least 80%, such as80-100%, 85-100%, 90-100%, 95-100%, or 95-99% over at least 100 cycles,at least 150 cycles, or at least 200 cycles. In any of the foregoing orfollowing embodiments, the lithium ion battery may have a capacityretention of at least 70%, at least 75%, or at least 80% after at least100 cycles, at least 150 cycles, or at least 200 cycles. In someembodiments, the capacity retention is 70-90%, such as 70-85%, after 200cycles. Advantageously, the cathode may be more stable (e.g., resistantto cracking) over extensive cycling, undergo fewer side reactions, beless moisture sensitive, and/or generate less gas during cyclingcompared to conventional Ni-rich cathodes (e.g., Ni≥0.6) prepared withpolycrystalline and/or monocrystalline NMC.

IV. Examples Example 1 Molten-Salt Synthesis and Characterization ofSingle Crystal LiNi_(0.76)M_(0.14)C_(0.1)O₂ (NMC76)

Synthesis

A Ni_(0.76)Mn_(0.14)Co_(0.1)(OH)₂ precursor was synthesized byco-precipitation method using a 5 L reactor at 55° C. Before theco-precipitation reaction, 1.5 L deionized (DI) H₂O and 65 mLconcentrated NH₃—H₂O (˜28 wt %) were added to the reactor and heated to55° C. as a starting solution. A 2 mol/L transition metal (TM) sulfatesolution (Ni:Mn:Co=0.76:0.14:0.10 in molar ratio) was prepared withNi(SO₄)₂.6H₂O, MnSO₄—H₂O, and Co(SO₄)₂.7H₂O, and then pumped intoreactor along with 8 M NaOH as well as 10 mol/L NH₃—H₂O buffer solution.The pumping rates of the TM sulfate and NH₃—H₂O solution were set at 3and 1 mL/min, respectively. The pH value was controlled at 11.2 duringreaction by adjusting NaOH adding rate. The synthesized precursor wasfiltered and washed by DI H₂O to remove impurities. After drying at 100°C. for 12 hours, the Ni_(0.76)Mn_(0.14)Co_(0.1)(OH)₂ precursor wasobtained. Ni_(0.76)Mn_(0.14)Co_(0.1)(OH)₂ was heated at 900° C. for 15hours in air to prepare the oxide precursor. The stoichiometry of theoxide precursor was analyzed by ICP-OES. The oxide precursor and lithiumoxide were mixed at 1:0.6 molar ratio (TM:Li=1:1.2), then NaCl (1:1.1weight ratio) was added to the precursor and mixed uniformly. Themixture was sintered at 800° C. for 10 hours and then 900° C. for 5hours using a 10° C./minute ramping rate in an oxygen atmosphere. Thesintered products were washed and dried at 80° C. in vacuum for 2 hours.Post annealing at 580° C. (10° C./min ramping) in oxygen atmosphere wascarried out before collecting the end products. Pure NaCl was used asthe molten salt media to lower the sintering time/temperature of thesingle crystals, thereby reducing the cost of synthesizing the singlecrystals.

Characterization

Scanning electron images (SEM) were collected on a Helios NanoLabscanning electron microscope (FEI, Hillsboro, Oreg.). Powder X-raydiffraction (XRD) data were collected at the 28-ID-2 (XPD) beamline ofthe National Synchrotron Light Source II (NSLS II), Brookhaven NationalLaboratory (BNL). A Perkin Elmer amorphous-Si flat panel detector wasused. The wavelength was 0.1821 Å. Pristine powder was loaded in Kapton®polyimide capillary tubes (1.0 mm diameter) in an Ar-filled glove boxand mounted on bases at the beamline. Rietveld refinement of the XRDdata was carried out in TOPAS6 (Coelho, J. Appl. Crystallogr. 2018,51:210-218). Transmission electron microscopy (TEM) specimen preparationwas conducted on a FEI Helios Dual-Beam FIB operating at 2-30 kV. TEMimages, selected area electron diffraction (SAED), high resolution TEM(HRTEM) images and scanning TEM energy-dispersive X-ray spectroscopy(STEM-EDS) were performed on a FEI Titan 80-300 S/TEM microscope at 300kV which was equipped with a probe spherical aberration corrector.HRSTEM high-angle annular dark-field (HRSTEM-HAADF) images andSTEM-electron energy loss spectroscopy (STEM-EELS) were performed on aprobe aberration-corrected JEOL JEM-ARM200CF microscope (JEOL USA,Peabody, Mass.) at 200 kV.

Since the TEM sample was very thin and self-absorption in the TEM samplewas negligible, EDS quantitation was performed by using a simple ratiotechnique (Cliff-Lorimer quantification). In this method, peakintensities are proportional to concentration and specimen thickness,and the effects of variable specimen thickness are removed by takingratios of intensities for elemental peaks and introduced a “k-factor” torelate the intensity ratio to concentration ratio:C _(A) /C _(B) =k _(AB) ·I _(A) /I _(B)  (1)Where I_(A) is Peak intensity for element A and C_(A) is concentrationin weight %. Each pair of elements requires a different k-factor whichdepends on detector efficiency, ionization cross section andfluorescence yield of the two elements concerned, k-factor kab iscalculated as follows:k _(ab)=(A _(a)ω_(b) Q _(b))/(A _(b)ω_(a) Q _(a))  (2)Where A_(a) and A_(b) are the atomic weights of elements giving rise tothe analytical lines a and b respectively, Q_(a) and Q_(b) are theionization cross sections of the shells, that once ionized give rise tothe analytical lines at the specified accelerating voltage. Thefluorescent yields ω_(a) and ω_(b) give probability of emission of thelines once the appropriate shell has been ionized. Once the k factor isknown, the element concentration in weight % can be calculated.

The as-prepared single crystalline NMC76 had a tap density of 2.12mg/cm³, while polycrystalline NMC76 is 2.08 mg/cm³. The increased tapdensity will benefit the cell-level energy due to the reduced porosityand improved electrode press density.

Electrochemical Test

To understand the electrochemical properties of single crystal NMC76 atindustry relevantscales, a cathode with reasonably high loading isneeded. However, half cells are not a good testing vehicle to evaluatehigh mass loading of the cathode materials due to the accelerated Limetal degradation when coupled with a thick cathode. Electrochemicalperformance was evaluated with 2032 type coin cells. Single crystallineMNC76 was mixed with carbon additive (C65 carbon black) and PVDF at96:2:2 weight ratio in NMP (N-methyl-2-pyriolidone) solvent and loadedon carbon coated Al foil. The areal loading of 5-26 mg/cm² electrodeswere prepared by adjusting the height of doctor blade. After drying at80° C. under vacuum, thick electrodes (˜20 mg/cm²) were calendared (˜32%porosity) and cut into Φ½ inch size discs for assembling cells. Prior tocalendaring, the porosity was 62%. Graphite powder was mixed with carbonadditive (C65), CMC and SBR at weight ratio of 94.5:1:2.25:2.25 andloaded on copper foil. The dried graphite electrodes were calendared andcut into Φ15 mm size discs. 1.0 M LiPF₆ in EC/EMC (3:7 weight ratio)with 2 wt % VC was used as electrolyte for both half cell and full celltests. Half cells were assembling using 450 μm thick Li metal as anode.Negative/Positive (N/P) ratio for full cells assembling was controlled1.15-1.2 (including ˜0.1 mg Li metal in graphite anode). In all the celltests, 1 C is named as 200 mA/g.

In Situ Electrochemical AFM Measurements (EC-AFM)

Fabrication of working electrodes for in situ EC-AFM: Aluminum (Al) foilwas chosen as the substrate because of its electronic conductivity andstability during the electrochemical cycles. The synthesized Ni-rich NMCsingle crystals were dropped on Al foil. Then the Al foil with Ni-richNMC was placed under a 5 tonnage press machine and held for 100 s. Theweakly bound and unfixed Ni-rich NMC crystals were removed by flowing N₂gas. The Al foil was then mounted onto the AFM sample holder with epoxyand an electrical contact was made to the bottom side of Al foil with aflattened nickel wire. Silicone grease was used to cover the outer rimof the O-ring to enhance the sealing of solution. The nickel wire wasisolated from solution due to the larger diameter of Al foil thanO-ring. The cell was ready for in situ AFM testing after cell assemblywith an O-ring, sealing cap with Li wire for the counter and referenceelectrode, and another free sealing cap.

All in situ EC-AFM images were captured in peak force or tapping mode atroom temperature (23° C.) with a Nanoscope 8 atomic force microscope (Jscanner, Bruker, Santa Barbara, Calif.) (Habraken et al., Nat Commun2013, 4:1507; Tao et al., PNAS USA 2019, 116:13867-13872). The AFM probeconsisted of silicon tips on silicon nitride cantilevers (HA_C Series ofETALON probes, k=0.26 N/m, tip radius <10 nm; K-TEK Nanotechnology,https://kteknano.com/product-category/etalon/). The electrolyte solutionof 1.0 M LiPF₆ in EC/EMC (3:7 weight ratio) was used as the testingsolution. A working cathode electrode (described above) was connected toSolartron 1287 electrochemistry workstation (Solartron, Farnborough,Hampshire, UK) by the nickel wire. A thin Li wire (counter and referenceelectrode) with sealing cap was inserted into the testing solution viaanother channel in liquid cell (Lv etai, Nano Lett 2017, 17:1602-1609).An electric signal was input into an AFM liquid cell with atwo-electrode configuration by a Solartron 1287 electrochemistryworkstation. The applied voltage started at OCV, increased up to 4.50 Vand down to 2.70 V with a uniform scan rate of 0.3 mV/s. For typicalimaging conditions, images were collected at scanning speeds of 1 Hz.

Several protocols were followed to ensure that the AFM images weretypical representations of the surface topography evolution. First, theimaging force was reduced to the minimum possible value (˜100 pN) thatstill allowed the tip to track the surface and no measurable effect ofthe scanning on the surface cracks. We verified this by zooming out to alarger scan box and comparing the crack number density with the smallerscan area. A consequence of imaging in the same area is that it maycause the less bound particles to move on the surface. This operationensures that the crack growth kinetics are minimally affected. Imageswere also collected at different scan angles and trace and retraceimages regularly compared to eliminate the possibility of imagingartifacts from tip contamination. The images were analyzed using theimage processing software package Nanoscope Analysis 2.0 (Bruker).

The average width of these steps almost linearly increases with thehigher voltage (vs. Li+/Li) during charging process followed by lineardecreases with the lower voltage during the discharge process, with itsvalue of 30.3±0.7 nm at open circuit voltage (OCV), up to 52.5±2.5 nm at4.50 V at charge status, and down to 38.4±1.3 nm at 4.19 V duringdischarge. The average step width is calculated by dividing the totalwidth of the lateral face by the total number of steps (between 21 and43 steps) for each voltage during the in situ AFM monitoring. The errorbars in the step width are evaluated by averaging of three times ofmeasurement of lateral face width at each time point.

Simulation

A cylindrical electrode particle diffusion-induced-stress model was usedhere along with material properties predicted by density functionaltheory (DFT) (28, 33). The particle is considered as an isotropic solidwith Young's modulus (E) increasing linearly with Li concentration. Inthe layered Ni-rich electrode, the diffusion of lithium ion is limitedin the two-dimensional channels, namely, between the layers, so lithiumdiffusion along the radial direction is assumed in the model. Thedimensionless particle size, time, Li concentration, and stress are usedfollowing the definitions in Deshpande et al., J Electrochem Soc 2010,157:A967-A971). For the parameters in simulation, α=0.0067; E₀=59.8 GPa;E=E₀+204.2 C; v=0.3 (Qi et al. J Electrochem Soc 2014, 161:F3010-F3018);and γ=2.1 J/m² was computed for Li₁₆(Ni₁₄CoMn)O₃₂ (Stein et al., ActerMater 2018, 159:225-240). The analytical solutions are provided in FIGS.29A-29D, 30A-30D. The numerical solution by COMSOL5.5 model is providedin FIGS. 31A-31D. For the anisotropic chemical strain solved in FIG.31D, the α=(0, 0, 0.02).

Results and Discussion

The synthesized NMC76 has a mean particle size of 3 μm (FIG. 7A). Across-section view (FIG. 17B) shows that NMC76 has a dense structurewithout cavities or grain boundaries. Pure phases of α-NaFeO₂-typelayered structures are confirmed by both selected area electrondiffraction (SAED, FIG. 7C) and X-ray Diffraction (XRD, FIG. 7D).Lattice parameters a and c are 2.8756(1) Å and 14.2221 (1) Å,respectively, from Rietveld refinement (Table 1). For comparison,polycrystalline NMC76 is found to contain many internal pores andintergranular boundaries along with surface films (FIGS. 8A-8F) formedfrom the reactions between NMC and air (Jung et al., J Electrochem Soc2018, 165:A132-A141). In contrast, the surface of single crystallineNMC76 is very uniform (FIGS. 7E and 7F). Elemental mapping (FIGS. 7G and7H) indicates a homogeneous distribution of Ni, Mn and Co with astoichiometric ratio as designed (Table 2). Continuous phase transitionshappen when potential changes (FIG. 9 ), similar to polycrystallineNMC76 (Zheng et al., Nano Energy 2018, 49:538-548). During charge, phasetransitions happen in the order of from H1 to M (H and M are hexagonalphase and monoclinic phase, respectively), M to H2, and H2 to H3,similar to polycrystalline NMC76.

TABLE 1 Rietveld refinement result of the pristine NMC76. a = 2.8756(1)Å, c = 14.2221(1) Å Atom Site x y Z Fraction Uiso Li 3a 0 0 0 0.986(1)0.004(1) Ni 3a 0 0 0 0.014(1) 0.004(1) Ni 3b 0 0 0.5 0.746(1) 0.005(2)Li 3b 0 0 0.5 0.014(1) 0.005(2) Mn 3b 0 0 0.5 0.14 0.005(2) Co 3b 0 00.5 0.1 0.005(2) O 6c 0 0 0.2403(1) 1 0.009(4)

TABLE 2 Elemental Ratio obtained from STEM-EDS Element Wt % Stdev Ni48.28 1.45 Mn 7.62 0.9 Co 6.98 1.13 O 37.12 1.69

Single crystalline NMC76 was further tested in graphite/NMC full cellsat realistic conditions. The typical loading of NMC76 cathodes is ca. 20mg/cm² (=4 mAh/cm²) with ca. 32% porosity, which is needed to build a250 Wh/kg Li-ion cell (Table 3). At such a high cathode loading, Limetal will worsen the cycling stability (FIGS. 10, 11 ) due to thedeepened stripping/deposition process of Li. Between 2.7 V and 4.2 V(vs. graphite), single crystalline NMC76 delivered 182.3 mAh/g dischargecapacity at 0.1 C, and retained 86.5% of its original capacity after 200cycles (FIG. 12A). With a cutoff of 4.3 V, single crystalline NMC76delivered 193.4 mAh/g capacity with 81.6% capacity retention after 200cycles (FIG. 12B). Further increasing to 4.4 V, 196.8 mAh/g dischargecapacity was seen (FIG. 12C) along with a 72.0% capacity retention after200 cycles. Note that 200 cycles at C/10 charge rate and C/3 dischargerate mean 2600 hours of cycling. The total testing time was equal to acell undergoing 1300 cycles at 1 C. Increased polarization (FIGS.13A-13C) was observed when the cutoff voltage increased which ispresumably assigned to intensified electrolyte decomposition at elevatedvoltages (FIGS. 14A-B, 15A-B, 16A-B) and thus higher impedance resultingfrom cathode passivation films and single crystal lattice change.Crystalline gliding and cracking were seen when the cutoff voltage wasbeyond 4.3V (FIGS. 13A-13C). Table 4 summarizes the electrochemicalperformances and testing conditions of all previously published singlecrystalline Ni-rich NMC (Ni>0.6) cathode materials.

TABLE 3 Cell design parameters for 250 Wh/kg lithium ion pouch cellbased on graphite/NMC76 chemistry MaterialLiNi_(0.76)Mn_(0.14)Mn_(0.10)O₂ Cathode 1^(st) discharge 200capacity/mAh g⁻¹ Active material loading 96% Cathode weight (each 21side)/mg cm⁻² Areal capacity (each 4.0 side)/mAh cm⁻² Electrode press3.0 density/g cm⁻³ Electrode thickness 70 (each side)/μm Number ofdouble 13 side layers Electrode dimension 36*54 W*L/mm Al foilThickness/μm 12 Anode Material Graphite Specific capacity/mAh g⁻¹ 360Active material loading 96% N/P ratio (cell balance) 1.16 Coating weight(each 13.5 side)/mg cm⁻² Electrode dimension 37.5*55.5 W*L/mm Cu foilThickness/μm 8 Electrolyte E/C ratio/g Ah⁻¹ 2.5 Separator Thickness/μm20 Packaging foil Thickness/μm 88 Cell Average voltage (1^(st) cycle)/V3.65 Capacity (1^(st) cycle)/Ah 2.0 Cell energy density/Wh kg⁻¹ 250

TABLE 4 Summary of single crystalline Ni-rich NMC (Ni > 0.6) reported inliterature Initial Capacity Cycling Capacity Voltage Retention Totalcycling Ref. Composition (mAh/g) Rate (V) Loading No. (%) Rate time(hr)* This LiNi_(0.75)M_(0.14)C_(0.1)O₂ 196.8 0.1 C 4.4 vs. Gr 20 mg/cm²200 72 0.1/0.33 C 2389 work (full cell) 1 LiNi_(0.8)M_(0.1)C_(0.1)O₂ 1850.1 C 4.2 vs. Li 3 mg/cm²  25 50 0.1/0.1 C ~500LiNi_(0.8)M_(0.1)C_(0.1)O₂ 240 0.1 C 4.6 vs. Li —  25 50 0.1/0.1 C 2LiNi_(0.58)M_(0.09)C_(0.03)O₂ 192 0.2 C 4.3 vs. Li 12 mg/cm² 100 880.2/0.2 C ~1000 (full cell) 3 LiNi_(0.8)M_(0.1)C_(0.1)O₂ 190 0.1 C 4.3vs. Li 3 mAh/cm² 100 ~90 1/1 C ~200 4 LiNi_(0.83)M_(0.08)C_(0.11)O₂184.1 1 C 4.2 vs 47 mg/cm² 600 84.8 1/1 C ~1200 Gr/SiO (tested at 45° C.full cell) 5** LiNi_(0.92)M_(0.01)C_(0.06)AlW_(x)Mo_(x)O₂ 221.4 0.1 C4.3 vs. Li 7.8 mg/cm² 100 95.7 0.5/1 C 100 *Testing time of singlecrystalline LiNi_(0.75)M_(0.14)C_(0.1)O₂ is captured from testing data.Testing time for reference results are evaluated according to thecurrent density. **x corresponds to 1000 ppm for W and Mo ¹Zhu et al., JMater Chem A 2019, 7: 5463-5474. ²Li et al., J Electrochem Soc 2019,166: A1956-A1963; ³Qian et al., Energy Storage Meter 2020, 27: 140-159;⁴Fan et al., Nano Energy 2020, 70: 104450; ⁵Yan et al., J ElectrochemSoc 2020, 167: 120514.

Lattice gliding was clearly observed in single crystalline NMC76 at highvoltages. Between 2.7 and 4.2 V (vs. graphite), the entire singlecrystal was well maintained after 200 cycles (FIG. 13A). Increasingcutoff voltage to 4.3 V, there were some gliding lines seen on thecrystal surfaces after 200 cycles (FIG. 13B). Cycled to 4.4 V, singlecrystals appeared to be “sliced” (FIGS. 13C, 17A-17F) in parallel, alongthe (003) plane and vertical to c-axis of the layered structure (FIG.18C), which indicated a model II type crack (in-plane shear) in fracturemechanics. Additionally, small cracks that indicate a model I typefracture (opening) were also discovered at 4.4 V (FIG. 13C). Allcharacterizations were done by selecting various regions of NMC76electrodes and the same phenomenon was repeatedly found (FIGS. 19-21 ).Although single crystalline NMC76 as a whole particle was still intact(FIG. 12A), gliding was the major mechanical degradation mode especiallywhen cutoff voltage is above 4.3 V. Of note, the “gliding steps” formedin cycled crystals are quite different from cracking along intergranularboundaries of polycrystalline NMC particles. The scanning transmissionelectron microscopy (STEM) image for single crystalline NMC76 (FIGS.18B-18D) confirmed that on both sides of a gliding plane (yellow line inFIG. 18D), the d-spacing of (003) plane (0.48 nm) was unchanged and thelayered structure was well maintained after the “gliding” marksoccurred. The long-range lattice symmetry of the bulk material willthereby not be altered. Ni, Mn, Co and O were still uniformlydistributed in the vicinity of glided planes based on electron energyloss spectroscopy (EELS) analysis (FIG. 18F and FIG. 22 ). The uniformelement distribution and intimately attached lattices across the glidingplanes strongly demonstrated that although planar gliding occurs, no newboundary was generated, and the “sliced” area maintained the samelattice structure and chemical conditions as in the bulk phase. Itshould be noted that the gliding line (or the slicing marks) cannot beobserved on the cross section of bulk particles by SEM, and are onlyvisible by STEM bright field (BF) on thin sliced TEM samples. Althoughthe internal lattice symmetry was well maintained after the gliding, therepeated gliding near surface eventually will evolve into microcracksexposing new surfaces to the electrolyte (FIGS. 13A-13C).

To further induce lattice gliding, the cutoff voltage of NMC76 singlecrystal is raised to 4.8 V (vs. □+/□). “Slicing marks” and microcracksare present in almost every charged single crystal (FIG. 23A). Slightdeformation of individual single crystals is clearly observed (FIG.18G), probably because the gliding of each layer equally likely movestowards symmetrically equivalent directions. Surprisingly, afterdischarging back to 2.7 V, the majority of single crystals revert totheir original morphologies and the previously observed steps andmicrocracks disappear (FIG. 23B). The “glided” layers within singlecrystals almost completely “glided” back to their original locations(FIG. 18H), fully recovering from the deformation (FIG. 18G), althoughsome “traces” are visible (labeled in FIG. 18H). Within the “regular”electrochemical window of 2.7-4.4 V (vs. graphite), after extensivecycling, lattice gliding and microcracking are also seen within crystallattice at charged status (FIG. 18I). STEM analysis of the NMC76 crystal(FIG. 18J) indicates that the microcracks initiate from inside of thecrystal. At the discharge status of those cycled crystals (cut off at4.4 V), few ridges or cracks are found on the crystals. Although not asvisible as in charged crystals, STEM still uncovers some “slicing marks”(FIG. 18K) on discharged single crystal NMC76 which probably undergoesreversible “sliding” process back and forth during 120 cycles. Nomicrocracking is identified in those “self-healed” single crystals (FIG.18L), suggesting that the lattice gliding and cracking in some of thecrystals are still reversible after 120 cycles. As cycling continues,particle deformation will become dominant. Dislocation was also observednear the tip regions of microcrack of single crystals charged at 4.4 V(FIGS. 24A-24D). The accumulation of dislocation was accompanied by themicrocrack propagation. A trace amount of nano-sized NiO-like rock saltphase (FIGS. 25A-25E) was observed on the gliding exposure step area ofsingle crystalline NMC76 after cycling.

In situ AFM has been used to image the crystal surface in real time inan electrochemical cell. A ˜3 μm sized NMC76 single crystal was studiedby in situ AFM during charge and discharge (FIGS. 26A-26F). Regions Band C in FIG. 26A are enlarged in FIGS. 26B and 26C, respectively, toprobe the origin and evolution of “gliding steps” and microcracks underthe electrical field. The formation of nanosized crack domains wasobserved on the side surface from open circuit voltage (OCV) to 4.50 V(vs. Li⁺/Li) during charge, while these domains disappeared in thedischarge process (FIG. 26B). Moreover, planar gliding was characterizedby the appearance of wide crystal steps on the side surface due to theuneven movement between neighboring layers during polarization. Morewide gliding steps were observed on the side surface starting at 4.20 Vcharging process and led to the more and wider (˜85 nm) gliding steps at4.50 V (FIG. 26C). When the cell potential decreased to 4.19 V, a fewwide gliding steps decreased in their width (FIGS. 27A-27B), indicatingthe atomic layer recovered back to their original position (FIG. 26C).The average width of the steps almost linearly increased with increasingvoltages (vs. Li+/Li) during the charging process followed by lineardecreases with decreasing voltages during the discharge process, withits value of 30.3±0.7 nm at open circuit voltage (OCV), up to 52.5±2.5nm at 4.50 V at charge status, and down to 38.4±1.3 nm at 4.19 V duringdischarge. The average step width was calculated by dividing the totalwidth of the lateral face by the total number of steps (between 21 and43 steps) for each voltage during the in situ AFM monitoring. The errorbars in the step width were evaluated by averaging of three times ofmeasurement of lateral face width at each time point. This “firstincrease then decrease” behavior of average step width vs. voltageindicates the reversible gliding process of these NMC crystals in eachcycle. The reversible gliding process is further illustrated in FIG.26F. The observed lattice gliding is a direct observation of the“Lattice-Invariant Shear (LIS)” (Radin et al., Nano Lett 2017,17:7789-7795). LIS should exist in many layered electrode materials,which experience stacking-sequence-change phase transformations due tolithium concentration change. It was also predicted that LIS will leadto particle deformation and ridges on the particle surface, but thesesignals are likely to be buried in the internal boundaries in aspherical-secondary polycrystalline. The micron-sized single crystalprovides a clear platform to observe gliding or LIS induced mechanicaldegradation.

Electrochemical potential difference is the driving force of lithium-iondiffusion and the formation of the lithium concentration gradient (Xiao,Sci 2019, 366:426-427). Stress will be generated during Li⁺ diffusionafter establishing a lithium concentration gradient in the lattice. Ananalytical cylindrical isotropic diffusion-induced stress model wasapplied to understand the stress generation when lithium ions diffusealong the radial direction in the particle. The analytical solution ofthe dimensionless principal tress along axial, tangential and radialdirections inside this cylindrical particle experienced compression ortension forces during cycling and reached maximum stresses when the Li+concentration gradient was the highest. The peak tensile stress alongtangential and axial directions occurred near the surface at the onsetof delithiation (or 0.01 T) (FIGS. 28A-28D). Conversely, the peaktensile stress in all three directions occurred at the center of theparticle (FIGS. 29A-29D) during lithiation. During charge(delithiation), the tensile stress along axial and tangential directionswas localized on the surfaces of single crystals, leading to microcrackopening normal to (003) planes. FIGS. 30A-30C are SEM images showingmicrocracks, which propagate from the center to the surface, formingfractures.

Local stress also has a shear component along other directions, which issolved numerically via COMSOL. The shear stress component along yzdirection that can trigger the gliding along the (003) planes is shownin FIGS. 20D and 20E. Although the signs of the shear stress duringlithiation and delithiation are opposite, which explains the reversiblegliding, the absolute values are not the same (FIGS. 31A-31D), since theelastic modulus is a function of Li concentration. Therefore, thegliding motion should be largely but not completely reversible. The peakstresses in FIGS. 31C and 31D are not exactly the same which providesthe explanation of the largely but not completely reversible gliding insingle crystalline NMC76 particles. Comparing the stress differencebetween FIGS. 31C and 31D, the anisotropic volume expansion (chemicalstrain) will lead to increased shear stress. The peak shear stresses areinside the particle during lithiation and delithiation, suggesting thesliding is likely to initiate inside of the particles. The irreversiblegliding can generate small damages, being accumulated into the crackopening over long time cycling, an analog of fatigue crack nucleation.These lead to the ridges and microcracks seen on the surfaces of singlecrystals after cycling.

The simple isotropic diffusion-induced-stress model can be used topredict if the cracks can be stabilized inside of the single crystal.Since the strain energy inside the particle reaches a maximum around thescaled time of Tp=0.1 T during delithiation (FIGS. 22A-22D), itscomparison with the fracture energy (2γ) is used as a criterion toevaluate the critical size of single crystal NMC76. If the accumulatedstrain energy is not large enough to cleave entire the crystal, thecrack will be stabilized inside of the particle.

$\begin{matrix}{{\prod }_{T_{p}} = {{\int{\frac{\sigma^{2}}{2E}dV}} = {{{\pi*h*\left\lbrack \frac{\alpha \star E_{0} \star \left( {C_{R} - C_{0}} \right)}{1 - v} \right\rbrack^{\underset{¯}{2}}} \star {\int_{0}^{r}{\xi^{2}\frac{1}{E}{rdr}}}} < {2\gamma}}}} & (1)\end{matrix}$where h is the height of the cylindrical particle, α is theconcentration expansion coefficient, E₀ is Young's modulus of thenonlithiated particle, E is Young's modulus at a given lithium-ionconcentration, C_(R) is the lithium-ion concentration at the surface, C₀is the lithium-ion concentration at the center, v is Poisson's ratio andξ represents the dimensionless stress (FIGS. 22A-D, 23A-D), and γ is thesurface energy, A lower bound estimation of the critical size of thesingle crystal is predicted to be ˜3.5 μm, below which cracks can beconsidered stable inside of the particle. The simulation result suggeststhat although fractures along (003) direction appear in single crystalsduring cycling, the cracks are stable once formed and will not initiatecatastrophic reactions to produce a fracture zone that eventuallypulverizes the entire single crystal. Increasing the applied currentdensity will lead to higher concentration gradient and higher stressgeneration. Increasing the cutoff voltage is equivalent to increasing(C_(R)−C₀) in equation (1). It means higher stress generation and largestrain energies at elevated voltages, which causes more “gliding” and“cracking” (FIGS. 7A-7C). The findings provide some strategies tostabilize single crystalline Ni-rich NMC by either reducing the crystalsize to below 3.5 μm, absorbing accumulated strain energy throughmodification of the structure symmetry, or simply optimizing the depthof charge without sacrificing much reversible capacity.

FIG. 32 shows an SEM image of a 20 μm single crystal NMC76 and imagesobtained by in situ AFM. Selective formation of a passivation film oncertain planes of the NMC76 was found. Dissolution and recrystallizationwere seen on surfaces of the single crystal. Parallel cracking along the[001] surface was directly captured.

Example 2 Molten-Salt Synthesis and Characterization of Single CrystalLiNi_(0.76)M_(0.14)C_(0.1)O₂ (NMC76)

Synthesis

A hydroxide precursor was prepared as follows. A 2 M solution oftransition metal (TM) sulfate solution (Ni:Mn:Co=0.76:0.14:0.10 in molarratio) was prepared in 805 g deionized water Ni(SO₄)₂·6H₂O, MnSO₄·H₂O,and Co(SO₄)₂·7H₂O. Separately 160 g NaOH was dissolved in 500 g H₂O.Concentrated NH₃—H₂O (28%) was diluted using DI H₂O at 1:1 volume ratio.1.5 L DI H₂O and 50 mL concentrated NH₃·H₂O (28%) were added into thereactor as the starting solution. The reactor was heated to 50° C. TheTMSO₄ solution, NaOH and NH₃·H₂O were pumped into the reactor at sametime. The pump rates were 3 mL/min and 1 mL/min for TMSO₄ and NH₃·H₂O,respectively. The pH was controlled at 11.0-11.5. When all TMSO₄solution was added into the reactor, the co-precipitated hydroxides wereaged in the reactor for hrs. The precipitates were filtered and washedwith DI H₂O ·200 g DI H₂O was used for every 100 g precipitates inwashing for 3-5 times. After drying at 100° C. for 12 hours, thehydroxide precursor Ni_(0.76)Mn_(0.14)Co_(0.1)(OH)₂ was obtained. Eachbatch produced ˜150 g of the hydroxide precursor.

The mixed hydroxide precursor was heated in air for 15 hours todecompose into mixed oxides. Three different temperatures, 800, 900, and1000° C., were used to study the influence of temperature on the oxideparticle size. The ramping rate was 5° C./minute. The morphology of thepristine hydroxide precursor and the oxides obtained at 800, 900, and1000° C. are shown in FIGS. 33A-33D, respectively. The optimalcalcination temperature was found to be 900° C. forNi_(0.76)Mn_(0.14)Co_(0.1)(OH)₂. Suitable temperatures range from400−1000° C.

The oxide precursors were mixed with Li₂O at 1:0.6 molar ratio(TM:Li=1:1.2), then the TM-Li mixture was mixed with sintering agentNaCl using a 1:1 weight ratio. The TM-Li—NaCl mixture was heated in atube furnace filled by flowing pure oxygen gas. The temperature wasincreased at 10° C./min ramping rate. The mixture was maintained at 800°C. for 10 hours, then at 900° C. for an additional 5 hours. The productwas cooled to room temperature. The sintered product (brick) was groundwith an agate mortar and then transferred to a beaker for washing awayNaCl. For each 15 g of sample, 30 g of water was added. The groundsample was stirred in water for two minutes. After ultrasonication for 2minutes, the mixture was stirred for an additional 10 minutes todissolve all residual NaCl. After filtration, the washed powders wereheated at 80° C. in vacuum for 2 hours to remove water. The driedsamples were further sintered at 580° C. in pure oxygen for four hoursto restore some lost oxygen in the lattices.

A schematic diagram of the process is shown in FIG. 34 . FIG. 34 alsoshows SEM images of the hydroxide precursor, the oxide precursor, andthe single crystal product.

In the absence of NaCl as a sintering agent, agglomerated ofLiNi_(0.76)Mn_(0.14)Co_(0.1)O₂ (NMC76) particles are formed instead ofsingle crystals. NaCl is an inexpensive sintering agent, lowering thecost for scaling up the synthesis. FIGS. 35A-35B are SEM images of NMC76prepared without NaCl sintering agent (FIG. 35A) and with NaCl (FIG.35B). Without NaCl, the sample was polycrystalline (FIG. 35A). WithNaCl, the sample was monocrystalline (FIG. 35B).

FIG. 36A shows the initial charge-discharge curve of NMC76 prepared withand without NaCl. FIG. 36B shows the cycling stability of a thick singlecrystal NMC76 electrode (20 mg/cm²) in a full cell using graphite as theanode between 2.7-4.2V, charge at 0.1 C and discharge at 0.33 C. 1 C=200mA/g. FIG. 36C shows the cycling stability of a single crystal NMC76electrode (21.5 mg/cm²) in a full cell using graphite as the anodebetween 2.7-4.3V.

Additional samples were prepared to compare washing with water and othersolvents. The samples washed with deionized water displayed the beststructural integrity and best electrochemical performance. FIGS. 37A and37B are SEM images of single crystal LiNi_(0.7)Mn_(0.22)Co_(0.08)O₂washed with water (37A) or formamide (FM) (37B). FIG. 37C shows theinitial charge-discharge curves of the two samples.

FIG. 38 is a schematic diagram comparing synthesis processes forpolycrystalline and monocrystalline LiNi_(X)Mn_(y)Co_(1-x-y)O₂. Whensynthesis proceeds directly from hydroxide precursors, a polycrystallineproduct is formed. However, when synthesis precedes via oxide precursorsas described herein, single crystals are obtained.

Example 3 Flash-Sintering Synthesis and Characterization of SingleCrystal LiNi_(0.76)M_(0.14)C_(0.1)O₂ (NMC76)

Synthesis

Hydroxide precursors were prepared as described in Example 2. Thehydroxide precursors and LiOH were mixed in a molar ratio of 1:1.2 andground with an agate mortar. The mixture was transferred to a flashsintering furnace and heated to 800° C. in a pure oxygen atmosphere atramping rates ranging from 2° C./minute to 20° C./minute. Thetemperature was maintained at 800° C. for 10 hours. No sintering agentwas used. Ramping rates up to 50° C./second or faster may be used.

FIGS. 39A-39C are SEM images of LiNi_(0.76)Mn_(0.14)Co_(0.1)O₂ preparedat ramping rates of 2° C./min (39A), 10° C./min (39B), and 20° C./min(39C). As the ramping rate increased, the particle size increased. Theagglomeration of particles was also significantly reduced when heatingrate was increased at 20° C., leading to the formation of large singlecrystals (FIG. 39C).

At a ramping rate of 2° C., however, the particles are mostly aggregatedtogether forming secondary particles instead of individual singlecrystals. A preheating process was found to facilitate flash sintering.Without wishing to be bound by a particular theory of operation,preheating reduces mismatch of reaction rates. The hydroxide precursorand lithium hydroxide mixtures were pre-heated at 480° C. for 5 hoursbefore flash sintering. During this pre-heating treatment, mixed oxides(including Li oxide) formed. It was also found that the NMC singlecrystals derived from preheated precursors demonstrated smaller particlesizes which improved the electrochemical kinetics of single crystal NMC.FIGS. 40A and 40B are SEM images of LiNi_(0.76)Mn_(0.14)Co_(0.1)O₂prepared without preheating (40A) or with preheating (40B) prior toflash sintering at a ramping rate of 50° C./minute. FIG. 41 shows thecharge-discharge curves of the single crystal NMC samples prepared withand without the preheating process, showing a clear improvement in thereversible capacity with preheating.

Example 4 Solid-State Synthesis and Characterization of Single CrystalLiNi_(0.76)M_(0.14)C_(0.1)O₂ (NMC76)

Synthesis

A hydroxide precursor was prepared as follows. A 2 M solution oftransition metal (TM) sulfate solution (Ni:Mn:Co=0.76:0.14:0.10 in molarratio) was prepared in 805 g deionized water using Ni(SO₄)₂·6H₂O,MnSO₄·H₂O, and Co(SO₄)₂·7H₂O. Separately 160 g NaOH was dissolved in 500g H₂O. Concentrated NH₃—H₂O (28%) was diluted using DI H₂O at 1:1 volumeratio. 3 L DI H₂O and 50 mL concentrated NH₃·H₂O (28%) were added intothe reactor as the starting solution. The reactor was heated to 50° C.The TMSO₄ solution, NaOH and NH₃·H₂O were pumped into the reactor atsame time. The pump rates were 3 mL/min and 1 mL/min for TMSO₄ andNH₃·H₂O, respectively. The pH was controlled at 10.8. When all TMSO₄solution was added into the reactor, the co-precipitated hydroxides wereaged in the reactor for 30 hrs. The precipitates were filtered andwashed with DI H₂O·200 g DI H₂O was used for every 100 g precipitates inwashing for 3-5 times. After drying at 100° C. for 12 hours, thehydroxide precursor Ni_(0.76)Mn_(0.14)Co_(0.1)(OH)₂ was obtained. Eachbatch produced ˜150 g of the hydroxide precursor.

The Ni_(0.76)Mn_(0.14)Co_(0.1)(OH)₂ was heated at 900° C. for 15 hoursin an oxygen atmosphere with a 10° C./min ramping rate. The hydroxideprecursors were converted to oxide precursors in this step.

The oxide precursors were mixed with LiOH at a Li:TM molar ratio of1:1.07 and annealed at 500° C. for 5 hours. The product was cooled toroom temperature and ground. A second annealing was performed at 800° C.for 5 hours. After grinding again at room temperature, a third annealingwas performed at 800° C. for an additional 5 hours. The final productwas passed through a 400-mesh sieve and collected.

FIGS. 42A and 42B are SEM images of the small particles ofNi_(0.76)Mn_(0.14)Co_(0.1)(OH)₂ and the Ni_(0.76)Mn_(0.14)Co_(0.1)O₂precursors, respectively. FIG. 42C is an SEM image of the single crystalLiNi_(0.76)Mn_(0.14)Co_(0.1)O₂. Use of small hydroxide precursorparticles facilitates synthesis of the desired monocrystallineLiNi_(0.76)Mn_(0.14)Co_(0.1)O₂. FIG. 43 shows the first charge anddischarge curve of the LiNi_(0.76)Mn_(0.14)Co_(0.1)O₂ at 0.1 C between2.7-4.4 V.

Cathodes comprising the monocrystalline LiNi_(0.76)Mn_(0.14)Co_(0.1)O₂prepared by the molten salt method of Example 2 and the monocrystallineLiNi_(0.76)Mn_(0.14)Co_(0.1)O₂ prepared by the solid-state method werecompared. FIGS. 44A and 45A show the charge-discharge curves of the twocathodes. The monocrystalline LiNi_(0.76)Mn_(0.14)Co_(0.1)O₂ prepared bythe solid-state method delivered ˜184 mAh/g. It is expected that furtherdevelopment will provide a reversible capacity of NMC811 single crystalsof >200 mAh/g, competitive with commercially available polycrystallineNMC, but with greatly enhance stability and safety. FIGS. 44B and 45Bare SEM images of the monocrystalline LiNi_(0.76)Mn_(0.14)Co_(0.1)O₂used in each cathode. The individual crystal size in FIG. 44B is ˜3 μm.The individual crystal size in FIG. 45B is ˜1 μm.

Example 5 Synthesis and Characterization of Single CrystalLiNi_(0.76)M_(0.12)C_(0.1)Mg_(0.01)Ti_(0.01)O₂

Synthesis

A hydroxide precursor was prepared as follows. A 2 M solution oftransition metal (TM) sulfate solution(Ni:Mn:Co:Mg:Ti=0.76:0.12:0.10:0.01:0.01 in molar ratio) was prepared in805 g deionized water using Ni(SO₄)₂·6H₂O, MnSO₄·H₂O, Co(SO₄)₂·7H₂O,MgSO₄, and TiOSO₄. Separately 160 g NaOH was dissolved in 400 g H₂O.Concentrated NH₃·H₂O (28%) was diluted using DI H₂O at 1:1 volume ratio.1.5 L DI H₂O and 50 mL concentrated NH₃·H₂O (28%) were added into thereactor as the starting solution and preheated to 50° C. The TMSO₄solution, NaOH and NH₃·H₂O were pumped into the reactor at same time.The pump rates were 3 mL/min and 1 mL/min for TMSO₄ and NH₃.H₂O,respectively. The pH was controlled at 11.5. When all TMSO₄ solution wasadded into the reactor, the co-precipitated hydroxides were aged in thereactor for 30 hrs at 50° C. The precipitates were filtered and washedwith DI H₂O·200 g DI H₂O was used for every 100 g precipitates inwashing for 3-5 times. After drying at 100° C. for 12 hours, Mg—Ti-dopedhydroxide precursors were obtained.

The doped hydroxide precursors were heated at 900° C. for 15 hours in anoxygen atmosphere with a 10° C./minute ramping rate. The hydroxideprecursors were converted to oxide precursors in this step.

The oxide precursors were mixed with Li₂O (1:1.4 molar ratio). NaCl wasthen added in a NaCl:TM-Li mixture of 1:1.1 by weight. The resultingmixture was then annealed at 800° C. for 10 hours and then 900° C. for 5hours. The product was cooled to room temperature. The sintered productwas ground with an agate mortar and then transferred to a beaker forwashing away NaCl. For each 15 g of sample, 30 g of water was added. Theground sample was stirred in water for two minutes. Afterultrasonication for 2 minutes, the mixture was stirred for an additional10 minutes to dissolve all residual NaCl. After filtration, the washedpowders were heated at 80° C. in vacuum for 2 hours to remove water. Thedried samples were further sintered at 580° C. in pure oxygen for fourhours to restore some lost oxygen in the lattices and provideLiNi_(0.76)Mn_(0.12)Co_(0.1)Mg_(0.01)Ti_(0.01)O₂, which includes 1 at %Mg and 1 at % Ti.

The modified single crystal has a slightly reduced particle size at ca.2 μm with a very dense structure (FIG. 46 ). The modified single crystalhas a reduced peak ration of (003)/(104), suggesting increased cationdisorder (FIG. 47A). Peak shifting to a lower angle in the modifiedsingle crystal indicates expansion of the crystal lattice compared topristine single crystal NMC76 (47B).

FIGS. 48A and 48B compare the charge-discharge curves (48A) and cyclingstability (48B) of LiNi_(0.76)Mn_(0.14)Co_(0.1)O₂ andLiNi_(0.76)Mn_(0.12)Co_(0.1)Mg_(0.01)Ti_(0.01)O₂. The modified singlecrystal NMC76 delivered at slightly slower capacity at ca. 191 mAh/gcapacity compared to the pristine single crystal NMC76 in a full celltested at relevant conditions—high mass loading and thick electrodes.The modified NMC76 displayed improved cycling stability with 81.8%capacity retention after 200 cycles, compared to pristine NMC76 with72.0% capacity retention. As shown in FIG. 49 , no obvious cracking wasobserved in the modified NMC76 after cycling.

Example 6 Pouch Cell Design

Table 5 provides parameters for 2.2-2.3 Ah pouch cells usinggraphite/NMC811 and graphite/NMC955 chemistries. Coin cells with similarcathode loading, areal capacity, porosity, press density, N/P ratio, andthe like, will be used for initial testing. Replacing graphite with Sior Li metal may increase the cell level energy to 300-350 Wh/kg with thesingle crystal NMC cathode.

TABLE 5 Cell design parameters for 2.2-2.3 Ah pouch cell designs basedon graphite/NMC chemistry Material NMC811 NMC955 Cathode 1^(st)discharge capacity (mAh g⁻¹⁾ 200 210 Active material loading 96% 96%Cathode weight (each side) 18.3 18.3 (mg cm⁻²) Areal capacity (eachside) 3.5 3.7 (mAh cm⁻²) Electrode press density (g cm⁻³) 3.0 3.0Electrode thickness (each 61 61 side) (μm) Number of double side layers*16 16 Al foil Thickness (μm) 10 10 Anode Material graphite graphiteSpecific capacity (mAh g⁻¹) 360 360 Active material loading 96% 96%Coating weight (each side) 11.4 12.0 (mg cm⁻²) Areal capacity (eachside) 3.9 4.1 (mAh cm⁻²) N/P ratio (cell balance) (μm) 1.12 1.12 Cu foilThickness/μm 8 8 Electrolyte Electrolyte/Capacity ratio 3.5 3.4 (g Ah⁻¹)Separator Thickness/μm 20 20 Packet foil Thickness/μm 88 88 Cell Averagevoltage (1^(st) cycle) (V) 3.65 3.7 Capacity (1^(st) cycle) (Ah) 2.2 2.3Cell energy density (Wh kg⁻¹) 250 264 *number of cathodes comprising Alfoil sandwiched between two NMC coating layers

In view of the many possible embodiments to which the principles of thedisclosed invention may be applied, it should be recognized that theillustrated embodiments are only preferred examples of the invention andshould not be taken as limiting the scope of the invention. Rather, thescope of the invention is defined by the following claims. We thereforeclaim as our invention all that comes within the scope and spirit ofthese claims.

We claim:
 1. A solid-state method comprising: making monocrystallinelithium nickel manganese cobalt oxide by heating a solid hydroxideprecursor comprising Ni_(X)Mn_(y)M_(z)Co_(1-x-y-z)(OH)₂ at a temperatureT_(S1) in an oxygen-containing atmosphere for an effective period oftime t₁ to convert the solid hydroxide precursor to a solid oxideprecursor; combining the solid oxide precursor with a molar excess of alithium compound; heating the solid oxide precursor and the lithiumcompound at a temperature T_(S2) for an effective period of time t₂ toproduce a first product; cooling the first product to ambienttemperature; reducing a mean particle size of the first product to 0.1μm to 10 μm; heating the first product having the reduced mean particlesize at a temperature T_(S3) for an effective period of time t₃ toproduce a second product; cooling the second product to ambienttemperature; reducing a mean particle size of the second product to 0.1μm to 10 μm; and heating the second product having the reduced meanparticle size at a temperature T_(S4) for an effective period of time t₄to produce monocrystalline lithium nickel manganese cobalt oxide havinga formula LiNi_(X)Mn_(y)M_(z)Co_(1-x-y-z)O₂, where M represents one ormore dopant metals, x≥0.6, 0.01≤y<0.2, 0≤z≤0.05, and x+y+z≤1.0.
 2. Thesolid-state method of claim 1, wherein: (i) the solid hydroxideprecursor has a mean particle size of 0.5 μm to 2.5 μm; or (ii) themonocrystalline lithium nickel manganese cobalt oxide has a meanparticle size of 0.5 μm to 5 μm; or (iii) the dopant metal M comprisesMg, Ti, Al, Zn, Fe, Zr, Sn, Sc, V, Cr, Fe, Cu, Zu, Ga, Y, Zr, Nb, Mo,Ru, Ta, W, Ir, or any combination thereof; or (iv) any combination of(i)-(iii).
 3. The solid-state method of claim 1, wherein: (i) thetemperature T_(S1) is 400° C. to 1000° C.; or (ii) the effective periodof time t₁ is 1 hour to 30 hours; or (iii) the temperature T_(S2) is400° C. to 1000° C.; or (iv) the effective period of time t₂ is 1 hourto 30 hours; or (v) the temperature T_(S3) is 600° C. to 1000° C.; or(vi) the effective period of time t₃ is 1 hour to 30 hours; or (vii) thetemperature T_(S4) is 600° C. to 1000° C.; or (viii) the effectiveperiod of time t₄ is 1 hour to 30 hours; or (ix) any combination of(i)-(viii).
 4. The solid-state method of claim 1, wherein heating thesolid hydroxide precursor at the temperature T_(S1) in theoxygen-containing atmosphere for the effective period of time t₁ furthercomprises: (i) increasing the temperature to the temperature T_(S1) at arate of 1-300° C./min, and heating the solid hydroxide precursor at thetemperature T_(S1) for the effective period of time t₁; or (ii) heatingthe solid hydroxide precursor in pure oxygen or air; or (iii) both (i)and (ii).
 5. The solid-state method of claim 1, wherein: (i) x=0.65-0.9,y=0.05-0.2, z=0-0.02, and x+y+z=0.7-0.95; or (ii) the lithium compoundcomprises lithium hydroxide, lithium carbonate, lithium nitrate, lithiumoxide, lithium peroxide, or any combination thereof; or (iii) the solidoxide precursor and the lithium compound are combined in a Li:solidoxide precursor molar ratio of 0.9:1 to 3:1; or (iv) any combination of(i), (ii), and (iii).
 6. The solid-state method of claim 1, furthercomprising preparing the solid hydroxide precursor by: preparing a1.5-2.5 M solution comprising metal salts in water, the metal saltscomprising a nickel (II) salt, a manganese (II) salt, a cobalt (II)salt, and optionally one or more dopant metal salts, wherein a molefraction x of the nickel (II) salt in the solution is ≥0.6, a molefraction y of the manganese (II) salt is 0.01≤y<0.2, a mole fraction zof the one or more dopant metal salts is 0≤z≤0.05, a mole fraction ofthe cobalt (II) salt is 1−x−y−z, and x+y+z≤1.0; combining the solutioncomprising metal salts in water with aqueous NH₃ and aqueous NaOH or KOHto provide a combined solution having a pH of 10.5-12 and a combinedmetal salt concentration of 0.1 M to 3 M; aging the combined solutionfor 5 hours to 48 hours at a temperature of 25° C. to 80° C. toco-precipitate hydroxides of nickel, manganese, and cobalt to providethe solid hydroxide precursor; and drying the solid hydroxide precursor,wherein the solid hydroxide precursor comprises particles having a meanparticle size of 0.5 μm to 2.5 μm.
 7. The solid state method of claim 6,wherein the metal salts are sulfates, nitrates, chlorides, acetates, ora combination thereof.
 8. The solid state method of claim 6, wherein themetal salts are sulfates, nitrates, or a combination thereof.
 9. Thesolid state method of claim 1, wherein: x is 0.7-0.9; y is 0.05-0.15; zis 0-0.02; and x+y+z is 0.7-0.95.
 10. The solid-state method of claim 1,wherein: the temperature T_(S1) is 800 ° C. to 1000 ° C.; and theeffective period of time t₁ is 10 hours to 20 hours.
 11. The solid-statemethod of claim 1, wherein: the temperature T_(S2) is 400 ° C. to 600 °C. and the effective period of time t₂ is 1 hour to 10 hours.
 12. Thesolid-state method of claim 1, wherein: the temperature T_(S3) is 700 °C. to 900 ° C.; and the effective period of time t₃ is 1 hour to 10hours.
 13. The solid-state method of claim 1, wherein: the temperatureT_(S4) is 700 ° C. to 900 ° C.; and the effective period of time t₄ is 1hour to 10 hours.
 14. The solid-state method of claim 1, wherein thelithium compound comprises lithium hydroxide.
 15. The solid-state methodof claim 1, wherein the solid oxide precursor and the lithium compoundare combined in a Li : solid oxide precursor molar ratio of 1.05:1 to1.5:1.
 16. The solid-state method of claim 1, wherein heating the solidhydroxide precursor at the temperature T_(S1) in the oxygen-containingatmosphere for the effective period of time t₁ further comprisesincreasing the temperature to the temperature T_(S1) at a rate of 1°C/min to 50° C/min, and heating the solid hydroxide precursor at thetemperature T_(S1) for the effective period of time b.
 17. Thesolid-state method of claim 1, wherein the monocrystalline lithiumnickel manganese cobalt oxide has a mean particle size of 1 μm to 5 μm.